Miss Crail has put up a fabulous post giving her reasons for hating Twitter, and even a month ago I would have agreed with her. Although it's uncluttered to look at, Twitter's interface makes it near impossible to follow discussions. Besides, there's a problem (for me) with its entire foundation - the question "What's happening?" (Hmmm, wasn't it "what are you doing?" They must have changed it to make it vaguely useful-sounding.) I'm going to cheat a bit here and just edit what I wrote in a comment on Miss Crail's blog.
That's exactly how I felt about Twitter first time round, and how I still felt until I started using JournoTwit. Now my feeds are displayed in nice, sensible columns with the hashtags I'm following separated nicely, with a column just for where I'm mentioned, and with a pretty feed cloud that I don't actually use much. I unfollow anyone who tells me too much about their mealtimes and transport arrangements, and use it mostly for following CPD-related topics. I have been converted.
I hate Twitter as it's set out on its own site - but with a decent reader it's actually very useful!
Re: Tom's comment - JournoTwit even has a handy "in reply to..." link that you can click on to see what a message was in response to. Doesn't work all the time, but it usually does - see screenshot above.