Twitter is acting up in a very strange way and has been doing so all weekend. Some tweets get through, some do not. It makes it look like an entire wave of Twitterers that I follow have gone on a Twitter vacation. I see Tweets from some and not from others.
What's weird, as MG Siegler points out is that we're not (as of the moment) getting any real communication from Twitter on the matter. It is amazing how addictive Twitter is, and I use it as my news stream throughout the day.
Hopefully things will get straightened out soon, or the withdrawal pangs will start to get pretty intense and drive the addicts elsewhere.