I think that Jsarnett “hits the nail on the head” in his comment:

Jsarnett’s Weblog: The more time I spend on Twitter, the more I begin to understand that it is much different than the other SNSs like MySpace and Facebook.  Twitter is not so in depth as these other sites.  Twitter is more of a place to stop and chat a bit on you way to somewhere else……image MySpace or Facebook being a party on the penthouse floor of the building….then Twitter is the elevator….complete with small talk and some occasional obligatory music to cover the silence. 

I find it interesting that one can only type 140 characters in Twitter which causes one to be short and directly to the point of what one is doing and/or thinking.  I do however like “small talk” because it makes for short reading but one of the biggest problems that I find is that if you aren’t on Twitter daily you can get lost very quickly in conversations (you are no longer in the “know”).