I keep blowing hot and cold with twitter, I've gone from cynical and anti, too pleasently surprised (mainly with a bit of help from our man Kip), but have recently relegated it to an auto tweet from this forum, mainly due to not having enough time.
But its interesting to occasionally logon, I average about 730 followers, it increases and decreases, but stays roughly about the same level. I seemed to have plateau'd
Disagree about facebook, we've tried it and got nothing. I think the audience arent as receptive to advertising as they are engaged in interacting with the actual site, as opposed to a more static site, where the advertising can signal a logical exit point.
I agree with Biz Angel about the content scrapers, people do get lazy when it comes to content, but good content will always be good content, be it on a blog, site or a tweet.