I have had a twitter account for a while, and as of this post I still have yet to make one tweet. To me, LinkedIn is a site with professional interaction whereas Facebook, MySpace, and Twitter are for social interaction. But the Twitter phenomena is not going anywhere considering that even LinkedIn has a place to tweet. I haven't used it, but I did notice one of my contacts use it to state that he was looking for a licensed mechanical engineer with HVAC experience. Now that has value. Telling me you are eating at a 5 & Diner and just had the best milk shake ever... not really worth my time.
But then I see that it worked for Shaq, and others as well in the engineering and CAD world. So I'm going to give it a shot. Don't expect too many tweets from me. My attendance is more of a social experiment. First matter of business, start following some people I know. Give me a shout if you are on twitter so I can follow you.