diff --git a/modules/_all/import.go b/modules/_all/import.go
index 5faf6e5..8833ca7 100644
--- a/modules/_all/import.go
+++ b/modules/_all/import.go
@@ -15,5 +15,6 @@ import (
 	_ "github.com/riking/marvin/modules/restart"
 	_ "github.com/riking/marvin/modules/rss"
 	_ "github.com/riking/marvin/modules/timedpin"
+	_ "github.com/riking/marvin/modules/usercache"
 	_ "github.com/riking/marvin/modules/weblogin"
 )
diff --git a/modules/usercache/database.go b/modules/usercache/database.go
new file mode 100644
index 0000000..29ab92c
--- /dev/null
+++ b/modules/usercache/database.go
@@ -0,0 +1,111 @@
+package usercache
+
+import (
+	"encoding/json"
+
+	"github.com/riking/marvin/slack"
+	"github.com/riking/marvin/slack/rtm"
+)
+
+const (
+	sqlMigrate1 = `CREATE TABLE module_user_cache (
+		user_id           varchar(15) PRIMARY KEY NOT NULL,
+		data              text
+
+		UNIQUE(user_id)
+	)`
+
+	sqlGetAllEntries = `SELECT * FROM module_user_cache`
+
+	// $1 = slack.UserID
+	sqlGetEntry = `SELECT data FROM module_user_cache WHERE user_id = $1`
+
+	// $1 = slack.UserID
+	// $2 = data (json encoded)
+	sqlUpsertEntry = `INSERT INTO module_user_cache (user_id,data) VALUES ($1, $2)
+		ON CONFLICT (user_id) DO UPDATE SET data = EXCLUDED.data`
+)
+
+func (mod *UserCacheModule) GetEntry(userid slack.UserID) (slack.User, error) {
+	var entry slack.User
+
+	var data string
+	stmt, err := mod.team.DB().Prepare(sqlGetEntry)
+	if err != nil {
+		return entry, nil
+	}
+	defer stmt.Close()
+	row := stmt.QueryRow(userid)
+	err = row.Scan(&data)
+	if err != nil {
+		return entry, nil
+	}
+	err = json.Unmarshal([]byte(userid), &entry)
+	if err != nil {
+		return entry, nil
+	}
+	return entry, nil
+}
+
+func (mod *UserCacheModule) LoadEntries() error {
+	stmt, err := mod.team.DB().Query(sqlGetAllEntries)
+	if err != nil {
+		return err
+	}
+
+	rtmClient := mod.team.GetRTMClient().(*rtm.Client)
+
+	defer stmt.Close()
+	var arr = make([]*slack.User, 200)
+	for stmt.Next() {
+		var id string
+		var data string
+		var user *slack.User
+
+		err = stmt.Scan(&id, &data)
+		if err != nil {
+			return err
+		}
+		err = json.Unmarshal([]byte(data), &user)
+		if err != nil {
+			continue
+		}
+		arr = append(arr, user)
+		if len(arr) >= 199 {
+			rtmClient.ReplaceManyUserObjects(arr, false)
+			arr = arr[:0]
+		}
+	}
+	if len(arr) >= 0 {
+		rtmClient.ReplaceManyUserObjects(arr, false)
+		arr = nil
+	}
+
+	return stmt.Err()
+}
+
+func (mod *UserCacheModule) UpdateEntry(userobject *slack.User) error {
+	return mod.UpdateEntries([]*slack.User{userobject})
+}
+
+func (mod *UserCacheModule) UpdateEntries(userobjects []*slack.User) error {
+	stmt, err := mod.team.DB().Prepare(sqlUpsertEntry)
+	if err != nil {
+		return err
+	}
+
+	defer stmt.Close()
+
+	for _, obj := range userobjects {
+		if obj != nil {
+			entrydata, err := json.Marshal(obj)
+			if err == nil {
+				_, err := stmt.Exec(obj.ID, entrydata)
+				if err != nil {
+					return err
+				}
+			}
+		}
+	}
+	return nil
+}
diff --git a/modules/usercache/usercache.go b/modules/usercache/usercache.go
new file mode 100644
index 0000000..3d6d568
--- /dev/null
+++ b/modules/usercache/usercache.go
@@ -0,0 +1,88 @@
+package usercache
+
+import (
+	"fmt"
+	"strconv"
+	"time"
+
+	"github.com/riking/marvin"
+	"github.com/riking/marvin/slack"
+	"github.com/riking/marvin/slack/rtm"
+)
+
+// interface duplicated in rtm package
+type API interface {
+	marvin.Module
+
+	GetEntry(userid slack.UserID) (slack.User, error)
+	LoadEntries() error
+	UpdateEntry(userobject *slack.User) error
+	UpdateEntries(userobjects []*slack.User) error
+}
+
+var _ API = &UserCacheModule{}
+
+// ---
+func init() {
+	marvin.RegisterModule(NewUserCacheModule)
+}
+
+const Identifier = "usercache"
+
+type UserCacheModule struct {
+	team marvin.Team
+}
+
+func NewUserCacheModule(t marvin.Team) marvin.Module {
+	mod := &UserCacheModule{
+		team: t,
+	}
+	return mod
+}
+
+func (mod *UserCacheModule) Identifier() marvin.ModuleID {
+	return Identifier
+}
+
+func (mod *UserCacheModule) Load(t marvin.Team) {
+	t.DB().MustMigrate(Identifier, 1505192548, sqlMigrate1)
+	t.DB().SyntaxCheck(sqlGetAllEntries, sqlGetEntry, sqlUpsertEntry)
+	t.ModuleConfig(Identifier).Add("last-timestamp", "0")
+	t.ModuleConfig(Identifier).Add("delay", (72 * time.Hour).String())
+}
+
+func (mod *UserCacheModule) Enable(team marvin.Team) {
+	go func() {
+		fmt.Printf("Loading user cache entries....\n")
+		err := mod.LoadEntries()
+		if err != nil {
+			fmt.Printf("Error whilst updating entries: %s\n", err.Error())
+			return
+		}
+
+		fmt.Printf("Loaded all entries from the user cache.\n")
+		go mod.UpdateTask()
+	}()
+}
+
+func (mod *UserCacheModule) Disable(t marvin.Team) {
+}
+
+func (mod *UserCacheModule) UpdateTask() {
+	rtmClient := mod.team.GetRTMClient().(*rtm.Client)
+
+	for {
+		timestr, _, _ := mod.team.ModuleConfig(Identifier).GetIsDefault("last-timestamp")
+		delaystr, _, _ := mod.team.ModuleConfig(Identifier).GetIsDefault("delay")
+		timeint, _ := strconv.ParseInt(timestr, 10, 64)
+		var timeres = time.Unix(timeint, 0)
+		delayres, err := time.ParseDuration(delaystr)
+
+		if err != nil || timeres.Before(time.Now().Add(-delayres)) {
+			fmt.Printf("Repolling user list....\n")
+			go rtmClient.FillUsersList()
+			err = mod.team.ModuleConfig(Identifier).Set("last-timestamp", strconv.FormatInt(time.Now().Unix(), 10))
+		}
+		time.Sleep(1 * time.Hour)
+	}
+}
diff --git a/slack/controller/channel_info.go b/slack/controller/channel_info.go
index 241b289..71a339a 100644
--- a/slack/controller/channel_info.go
+++ b/slack/controller/channel_info.go
@@ -189,8 +189,15 @@ func (t *Team) cachedUserInfo(user slack.UserID) *slack.User {
 
 	uID := slack.ParseUserMention(string(user))
 	if uID != "" {
-		go t.updateUserInfo(user)
+		// XXX HACK to get around unlocking.
+		t.client.MetadataLock.RUnlock()
+		defer t.client.MetadataLock.RLock()
+		user, err := t.updateUserInfo(user)
+		if err == nil {
+			return user
+		}
 	}
+
 	return nil
 }
 
diff --git a/slack/controller/team.go b/slack/controller/team.go
index 8022a18..07ef4f3 100644
--- a/slack/controller/team.go
+++ b/slack/controller/team.go
@@ -8,6 +8,7 @@ import (
 	"net/http"
 	"net/url"
 	"os"
+	"strconv"
 	"strings"
 	"sync"
 	"time"
@@ -318,7 +319,13 @@ func (t *Team) SlackAPIPostJSON(method string, form url.Values, result interface
 		util.LogBadf("Slack API %s error: %s", method, err)
 		util.LogBadf("Form for %s: %v", method, form)
 		if slackResponse.SlackError == "ratelimited" {
-			time.Sleep(1*time.Second)
+			retryafter := resp.Header.Get("Retry-After")
+			intp, err := strconv.ParseInt(retryafter, 10, 64)
+			if err == nil {
+				time.Sleep(time.Duration(intp) * time.Second)
+			} else {
+				time.Sleep(1 * time.Second)
+			}
 		}
 		return errors.Wrapf(err, "Slack API %s", method)
 	}
diff --git a/slack/rtm/events.go b/slack/rtm/events.go
index f3047a0..bd0f047 100644
--- a/slack/rtm/events.go
+++ b/slack/rtm/events.go
@@ -90,6 +90,13 @@ func (c *Client) onChannelJoin(msg slack.RTMRawMessage) {
 }
 
 func (c *Client) ReplaceUserObject(obj *slack.User) {
+	var cacheApi userCacheAPI
+	moduleCacheApi := c.team.GetModule("usercache")
+	if moduleCacheApi != nil {
+		cacheApi = moduleCacheApi.(userCacheAPI)
+		cacheApi.UpdateEntry(obj)
+	}
+
 	c.MetadataLock.Lock()
 	defer c.MetadataLock.Unlock()
 
@@ -103,7 +110,14 @@ func (c *Client) ReplaceUserObject(obj *slack.User) {
 	c.Users = append(c.Users, obj)
 }
 
-func (c *Client) ReplaceManyUserObjects(objs []*slack.User) {
+func (c *Client) ReplaceManyUserObjects(objs []*slack.User, updateCache bool) {
+	var cacheApi userCacheAPI
+	moduleCacheApi := c.team.GetModule("usercache")
+	if moduleCacheApi != nil && updateCache {
+		cacheApi = moduleCacheApi.(userCacheAPI)
+		cacheApi.UpdateEntries(objs)
+	}
+
 	c.MetadataLock.Lock()
 	defer c.MetadataLock.Unlock()
 
diff --git a/slack/rtm/membership_info.go b/slack/rtm/membership_info.go
index 542897d..08efd59 100644
--- a/slack/rtm/membership_info.go
+++ b/slack/rtm/membership_info.go
@@ -5,6 +5,7 @@ import (
 	"time"
 
 	"github.com/pkg/errors"
+	"github.com/riking/marvin"
 	"github.com/riking/marvin/slack"
 	"github.com/riking/marvin/util"
 )
@@ -16,6 +17,13 @@ type membershipRequest struct {
 	C chan interface{}
 }
 
+type userCacheAPI interface {
+	marvin.Module
+
+	UpdateEntry(userobject *slack.User) error
+	UpdateEntries(userobjects []*slack.User) error
+}
+
 func (c *Client) membershipWorker() {
 	for req := range c.membershipCh {
 		req.C <- req.F(c.channelMembers)
@@ -141,13 +149,12 @@ func (c *Client) ListIMs() []*slack.ChannelIM {
 
 func (c *Client) fetchTeamInfo() {
 	go c.fillGroupList()
-	go c.fillUsersList()
 
 	// TODO(kyork): list normal channels too
 	// TODO(kyork): use the listChannels() from logger module
 }
 
-func (c *Client) fillUsersList() {
+func (c *Client) FillUsersList() {
 	var response struct {
 		slack.APIResponse
 		Members  []*slack.User
@@ -165,16 +172,17 @@ func (c *Client) fillUsersList() {
 		util.LogError(errors.Wrapf(err, "[%s] Could not retrieve users list", c.Team.Domain))
 	}
 
-	for response.PageInfo.NextCursor != "" {
-		c.ReplaceManyUserObjects(response.Members)
-		time.Sleep(2*time.Second)
+	c.ReplaceManyUserObjects(response.Members, true)
 
+	for response.PageInfo.NextCursor != "" {
+		time.Sleep(2 * time.Second)
 		form.Set("cursor", response.PageInfo.NextCursor)
 		err := c.team.SlackAPIPostJSON("users.list", form, &response)
 		if err != nil {
 			util.LogError(errors.Wrapf(err, "[%s] Could not retrieve users list", c.Team.Domain))
-			break
+			continue
 		}
+		c.ReplaceManyUserObjects(response.Members, true)
 	}
 }