<< Now, we're happy to announce that Offline Gmail is graduating from Labs and becoming a regular part of Gmail. If you're already using it, then you're all set. While you'll no longer see it on the Labs tab, you can tweak your settings and turn it on and off from the Offline tab under Settings. >>

http://gmailblog.blogspot.com/2009/12/offline-gmail-graduates-from-labs.html

This doesn't really fit in with the "Google is killing Gears" rumours going round last week :P