What this means for Mac users: better support for Gmail within Mail.app, Thunderbird and Entourage. For iPhone users: a way better Gmail experience over the previous POP or web client approaches -- Gmail has even posted handy setup instructions for you. First step: Don't choose the Gmail setup button, choose "Other..." instead. (Yes, they know, they're working on it.)
If you use Gmail and want to fire it up in IMAP on your iPhone, by all means let us know how it goes.