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.
People on irc
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.