I'd just like to say well done on the implementation of Slack.
I requested an invite to the ACC team on Slack because we use the tool at work. For instant collaboration it's pretty nifty,
Slack offers a lot of IRC-like features: persistent chat rooms (called channels), as well as private groups and direct messaging. Everything posted inside Slack is searchable, including files, conversations, and people and it can also be used with Google Drive, Dropbox and Box for file sharing.
Exciting times ahead, now all we need are people to join and use it.