For me, Twitter is my social messaging platform of choice. In truth, I could live without any other social messaging platform, but I’ve come to depend on Twitter for communication with a large number of people that I value. In addition, if Twitter had certain features built in, I could live without some of the other sites which have been developed to integrate with Twitter. For example: if there were a direct way to post photos to Twitter, I’d probably not use Brightkite, even though I like the “idea” of location based social networking and that concept might come into it’s own in one form or another.
Other social messaging sites I use:
Interesting social messaging aggregator, Dipity.com. Dipity pulls your feeds into a timeline, seen below.