Mono is a distributed effort with developers scattered around the globe, although a lot of discussion happens on the public mailing lists, some interactive discussion happen on IRC.
Network: Gimpnet (servers: irc.gnome.org, irc.gimp.net)
- #mono: general discussion of Mono.
- #monodev: discussion more geared toward development.
- #mono-winforms: development of the Windows.Forms stack.
- #monodevelop: Chat related to the MonoDevelop IDE.
- #mono-hispano: general discussion of Mono (in spanish).
- #monouml: general discussion of MonoUML.
- #gendarme: discussion, mostly development oriented, about Gendarme
- #mono-a11y: Accessibility and UI Automation
- #moonlight: discussion on the Moonlight implementation of Silverlight.
- #monotouch: Discussion on Mono for the iPhone, MonoTouch
- #monodroid: Discussion of Mono on the Android, 
- #monomac: Discussion of the MonoMac bindings for Mono on OSX
Network: OFTC (servers: irc.oftc.net)
- #debian-cli: Packaging Mono and related software for Debian, Ubuntu and other Linux distributions.
There are a lot of people. Some of them might not be alive (sleeping). If you have questions to ask, don't be afraid and feel free to ask them. (It is encouraged just to write your questions. No need for excuse.)
There are various IRC clients available, here are some recommendations: