The have the help pages up already, see

http://gmail.google.com/support/bin/answer.py?answer=13273

but it certainly does not seem to be enabled for my account. Probably, like the notifier, they are only rolling it out a few accounts at a time.

Reported at http://www.gadgetgossip.com/archives/2004/11/98/ and live in my account – I haven't tried it yet!

This page explains that its going to be weeks until this feature is rolled out to all users:

http://gmail.google.com/support/bin/answer.py?answer=13294&topic=194

I got a GMAIL enabled acct. I'm excited to use it with Mozilla Thunderbird.