We have an IRC channel, #microformats on the freenode network.
There's typically someone there at any point during the day, though there isn't always active discussion. Sometimes, though this is the best place to discuss issues that need lots of back and forth discussion.
To display a brief description of who you are each time you join the channel, you can create a definition for your username. To do so pass the ?def command using something like the following convention (be brief):
?def jdoe is John Doe and can be found online at http://www.jdoewebsite.com
More information about using JiBot commands can be found on the jibot website
Available here: http://rbach.priv.at/Microformats-IRC/
Atom feed of logs available here: http://microformat.makedatamakesense.com/log_feed/
The idea of having IRC meetups (that is, a set time for meeting on IRC) has been suggested by Ryan King, as it appears to work well for the WordPress community and may help us from time-to-time. As of yet, there are no plans to have meetups, though.