Some of the development of MapServer is coordinated through IRC. This page describes how you log on to chat, ask questions, and hack around with the developers.
Server: irc.freenode.net
Channel: #mapserver
Logs: http://logs.qgis.org/mapserver/
IRC is a primary medium where Open Source GIS hackers congregate, collaborate, and hack. It makes it easy to communicate things like compilation issues, where immediate, iterative feedback allows folks to make a lot of progress. Something that might take days of heavily-quoted emails through a maillist might only take fifteen minutes on IRC.
IRC is a great way to coordinate on-line meetings. Much of the discussion about the development of the new MapServer website was coordinated through IRC.
Some folks find IRC distracting and do not normally participate except for on-line meetings.
Chatzilla is probably the easiest way to get going. Chatzilla works with Mozilla or Firefox, and once you have it installed, you can log on to the channel by pointing your browser at:
irc://irc.freenode.net/#mapserver
There are many other IRC clients available. This page provides a good listing for many different platforms.