I follow mainly some people from here, plus a bunch of journalists and a couple of prominent tech people.
Getting personal replies to questions from the likes of Jon Honeyball (who generally provides very useful information) or David Pogue makes the whole experience feel like it is a level playing field.
I regularly prune my follow list. If somebody starts just posting links to websites and not "contributing", I'll stop following them (a couple of magazines or news feeds being the exceptions). In fact, with the people I follow, I find I generally use Twitter instead of an RSS feed these days.
Facebook on the other hand really doesn't seem to attract me.
I think that the difference, for me, is that with Twitter, you can dip in and out of it, you can get quick responses (also from people who aren't following you) to real questions - I had problems de-installing an old AV product at work last weekend and Saspro and a couple of other people had useful information, when it stopped playing ball...
Getting instant answers like that doesn't work with a forum or Facebook.
That said, I wouldn't follow most celebrities (I follow Mr Fry and a couple of others (who barlely post), but none of the mega celebrities who tweet garbage all the time).
An interesting one was Brent Spiner, he tweeted a complete story about being held hostage and tortured over 2 or 3 days. It was entertaining, as were his replies to people asking questions or telling him to get a life!
That was the first Twitter event that I've seen, it was very unique and very interesting.
