I use it a LOT more since I installed TwitterFox as it's just "there" all the time.
My primary use of it is for status updates from my servers and to let me know when something happens on a website ... "@woodss A booking has been made on %website% - check the order system" or "@woodss There was a failure on doUpdate.asp, line 59 - database connection refused" or something like that.
You have to learn how to hook your code into the Twitter API though, but it IS totally useful once you give it a chance. I think everyone i've known has said "whats the point" and now they use it as if they always have; I know I was a doubter at first too.
Seriously though, TwitterFox makes it useful.