Google announced GMail IMAP support on 10/24 at 6am. That was a little over 5.5 days ago.
Not to sound ungrateful, but you can’t announce a huge feature like that and then, you know, not deliver it. The announcing blog post even uses the beautifully indeterminate “couple of days” timeframe which, depending on your regional predications, could mean anywhere from 2 to however-many-we-feel-like days.
Ah well, when (or, if) it shows up I’ll be fine. The things you can get away with when you’re a monolithic corporation.
UPDATE (10/31): It showed up tonight; IMAP kicks ass.