The have the help pages up already, see

gmail.google.com/support/bin/a ...

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 gadgetgossip.com/archives/2004 ... 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:

gmail.google.com/support/bin/a ...

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