Have set up a Twitter account today and have tried searching to see what may be of interest. At first impression, it looks like a device to seize what shreds of personal time may be left in my life. I did not choose to tell Twitter my email address or (imagine!) mobile phone number. Imagine being bombarded via phone or email with mindless announcements of what your "friends" are doing now.
However, I have an interstate colleague who is a librarian webwriter/writer/magazine editor, who told me she is quite excited about Twitter. I have just found her on Twitter, and have clicked to "follow" her. I see that she is using Twitter in a very business-like way, to make announcements about developments in the field of youth studies, which she works in. So it may also have useful possibilities. I guess it is quicker than blogging, and more interactive, more like chat in fact.
I have called my Twitter account "Bats in a fig tree".