I just founded #graffitio on freenode so we have an IRC channel to call our own. The server is irc.freenode.net and the channel is #graffitio. I’ll be there most of the day if you have any questions, and I’m hoping it’ll be a good place to get to know other Graffitio users (outside of Graffitio itself, of course).
On a Mac, Colloquy is an excellent freeware client. On Windows, Trillian is a popular client that many of you may already use for IM. On *nix, GAIM and X-Chat are two of dozens of clients you have to choose from. Once you get a client setup, this link should take you straight there:
mibbit.com for Orc on iPhone
irc not Orc http://mibbit.com