You can use it to create public and/or private chat rooms and send private messages, all of which make it suitable for collaboration, in-depth discussions, and some good, old-fashioned procrastination (e.g., sharing animated gifs). The just-released File API opens up even more possibilities for the tool.
There are Patter rooms dedicated to fitness, users of specific App.net clients, and pitching ideas for App.net applications. We even have incorporated Patter into our developer support. Last weekend, the #ADNComicsClub used Patter as a forum for the discussion and the #MondayNightDanceParty crew integrate it into their weekly madness. Word is spreading fast about its addictiveness.
You can create your very own Patter room here.