This sort of behavior is not acceptable to me. I do not want to have separate applications or separate bookmarks that I have to check for the updates on each of twitter, tumblr, youtube, blogspot, wordpress, etc. that I wish to follow; I want as many of them as possible in one place. That is exactly what RSS/Atom are for. And, the low signal-to-noise ratio of a lot of the content on twitter (sorry, but it's just not possible to go into much depth in 140 characters, and much of the content there simply provides alternative links to stuff I'd already found elsewhere) means that it's not important enough to me to find an alternative way to read it.
So goodbye, @cstheory, and all the other theory twitterers, and goodbye, twitter.
ETA: False alarm. Twitter is still phasing out rss feeds, and I still think that's a bad thing, but there are still feed urls (different than the ones I had been using) that work for now.