Sometimes I wonder if I would be using Twitter if I didn't have a blog. I enjoy it and do get into some fun conversations, especially during "events", I use it mainly for marketing purposes. I just reviewed a great book on Twitter called Twitter Power http://connectwithyourteens.blogspot.com/2009/03/twitter-power-book... which gives great insight into using twitter for marketing. However, sometimes I think I should stop making everything about marketing and forget I have a blog once in a while.
I use Twitter for both. But I keep my personal tweets and business tweets separate now by keeping two accounts. My personal tweets are here: http://twitter.com/NissaG, and my business tweets (my publishing company) are here: http://twitter.com/PartridgeHill
Don't want to alienate my friends with lots of business tweets.
I personally twitter whatever happens to cross my mind, but I don't find it a very interactive platform. Sometimes it seems like a bunch of screams out into the universe and there's no one really there to catch them. I tweet about whatever and if someone happens to reply, I try to develop a dialogue with them. I would like twitter to be more engaging with conversations that are easier to follow. The forums are too difficult to follow, there should be a twitter space for that. Just my two cents.
I also have a business twitter account and use that for business purposes - marketing, promotions, etc.