HEY! I'm not sure if this means my gmail account is pushing, but I've been getting all my emails from my gmail account almost a minute after they are being sent. I sent several test messages to my account and all give me the same result.
I don't have mobile me, do not have an exchange account, and was fully relying on my phone to pull emails every hour on a fetch schedule. Now i'm getting them almost immediately after the emails are sent.
Gmail in Mail seems to run imap IDLE while the phone is being used or if a connection to the server after checking mail still exists (haven't confirmed which it is), but it definetly doesn't push when the phone is sitting idle for long periods of time.