I've written about the flash-mobby nature of Twitter before. I think it's important to note that these types of event are happening more and more frequently and with more and more ease. Nonetheless, Twitter's not the ideal tool for planning regular meetings -- Meetup is by far the best tool for the job.
What's my point? Just like the Ambience Scatter* concept I put forth on Jeremy Wagstaff's blog (messages find the right medium, fracturing more and more as better tools address niche message-types), I'm now playing with a concept called "Scatter Mob" which also deals with the questions of which tool is best for what kind of get-together.
What are your thoughts?
*My Ambience Scatter concept was inspired by Leisa Reichelt's influential post about Ambient Intimacy. That's required reading!