The update -- which is now freely available in the App Store -- allows you to sign into one or several Google accounts and set up Gmail and Google Calendar push events, which work just as you'd expect. It's not yet clear how consistently quick the app is at alerting you of new mail, though it seems to have a significant delay upon initial testing. So far connectivity to my Gmail account using the Mail app responds much quicker.
As you can see from the screengrab of the update, you can specify quiet times for notifications, which could be handy if you tend to get a deluge of mail in the wee hours of the night. Google customers rejoice: push notifications are finally here!