Results from tweet search are delayed several hours and we are working on the underlying problem.

The rest is here:

Working on stale search results

We are investigating reports of users receiving invalid responses from the API

Visit link:
Investigating invalid responses from the API

Users using certain Twitter clients are unable to Log in.

These clients include

- HTC Peep

- Moto BLUR

- Nokia Twitter apps

- Samsung devices (except for phones running Android OS)

- Huawei phones 

We are working to resolve this issue.

Follow this link:

Log-in issues for users of some mobile clients

We are performing some scheduled maintenance on the site; you may experience periods of elevated errors.

See original here:

Potential Errors Due to Maintenance

We’ve temporarily turned off the “Who To Follow” feature and will be restoring it as soon as possible. We were including people you already follow – we are investigating this issue.

Update at 2:15PM: This issue has been resolved.

Continue reading here:
Temporarily Disabling "Who to Follow"

There is an issue with the API that is causing some clients to crash. A fix is being deployed now

See the original post:

A known API issue is causing some clients to crash

The mentions timeline is frozen; engineers are working on the issue now.

Update: this issue has been resolved.

Link:
Mentions Timeline Frozen (@ replies)

Some features are intermittently not available on Twitter at this time. 

- Ability to Follow a user

- Follow counts

- Sending DMs

Twitter is working to resolve this issue in full.

Read the rest here:

Follow, Follower Counts and DMs Intermittently inaccessible

Lists and Tweet counts on the home page are currently disabled; we’re working toward restoring them. You can still see your total number of Tweets on your profile page.

UPDATE: Lists and Tweet counts on homepage is estimated to be restored by 6AM PDT.

Continue reading here:
Lists and Tweet Counts are Currently Disabled

We’re currently experiencing a high error rate on Twitter. Our infrastructure and operations engineers are responding to the incident.

Update:  Thu Aug  5 22:39:04 UTC 2010: Twitter is currently recovering, Tweets are are flowing again. We expect a full recovery in the next hour.

Update: Thu Aug  5 23:46:11 UTC 2010: Twitter is fully recovered.

Link:

We’re currently experiencing a high error rate on Twitter.