Wetpaint, the wiki editing and hosting service, added private and group messaging this morning. The new service allows users to communicate one-on-one just like e-mail, and gives wiki administrators a new way to communicate to those moderating and contributing to their pages.
Sending a message in the service is pretty simple. If you're signed in, just click a user's name to pull up a "send message" pop-up. If you want to send out a group message, just start typing in names and the service will pull them up (like Gmail does).
In comparison, wiki juggernaut Wikipedia relies on private e-mail and threaded discussion called "Talk" for member-to-member communication. That site also has dedicated IRC chat rooms and a listing of chat client screen names for Wikipedia contributors. Wetpaint's new system makes things a little simpler by consolidating chatter into one medium, and integrating it into the site.