Ok, after a little thought, here's my revised take on Twitter.
Twitter appears to be a hosted blog service. Nothing more nor less. The only thing innovative about it is that it limits your postings to 90 characters, and thus encourages you to post less, more frequently. Since I already have a blog, if people want to subscribe to my RSS feed, well, I've already got one. And it doesn't limit me to 90 characters. If I can say something in 90 characters, it probably wasn't worth saying.
Well, your post was 88 words. Or, 400 characters w/o spaces. THIS comment is a full 90 cha