[EDIT] Shoot - just found an old blog post about this elsewhere. Guess I missed when they enabled this a while back. I feel really smart now![/EDIT]
I was playing with an Android emulator this weekend and noticed that when I set up an Exchange account to synchronize my calendar and contacts with Google, I also started seeing email notifications. I thought that Android might just be acting "smart" and adding an IMAP account based on the same credentials. So, to verify this, I went to the Exchange account on my iPhone that also syncs to Google contacts/calendar and enabled the Email switch. Lo and behold, I now had a working email exchange account from the Mail app! I sent myself a few emails from other accounts, and got a new mail notification on the iPhone within an average of five seconds. I looked around and did not see any reference to this being enabled, so maybe this is in preparation for the likely Nexus One release announcement at tomorrow's Google Android event. Either way, I hope this feature stays enabled since having real push GMail on the iPhone is really handy!