It sounds like its just another version of Facebook. Personaly, I am not adicted to a blackberry, cellphone with data service (internet), or a PC enough to use the "updating (what am I doing/ what are you doing) properties of these programs. In plain english, I would rather spend time away from work out shooting targets (not shooting the shi*).
The short version of Twitter is that it's an adaptation of the blog. Where it comes in handy is with wireless devices that don't allow for easy typing. You can post messages to it very quickly using a cell phone or wi-fi device and other people can "follow" you and find out when you've posted something.
I'll admit I didn't see the usefulness of it to begin with - until the most recent Apple show, where one group (I believe it was Engadget?) covered it really effectively and quickly using Twitter. Another possible use would be to follow USA Carry's Twitter page and see a constant stream of new posts on the forum.