I spoke to Daren G on mobileMe support and he recommended trying this:
1.) Push the Home button on the iPhone.
2.) From the Home menu tap the Settings icon and then select Fetch data.
3.) Toggle Push to off and Power cycle the phone(power off iPhone for 30seconds to a minute. Then turn the phone back on.)
4.) When at the Home menu tap Settings, then select Mail, Contacts, and Calendars. From here select the Mobile Me account. At the very bottom go ahead and delete the Account.
5.) Add the account back to the iPhone. Make sure to use "@me.com" and then from the Home screen select Settings and then Fetch new data. Turn the option for Push back on and power cycle the phone once again.
6.) When the iPhone starts back up, send test email to yourself. It can take a few minutes to arrive. Once it does, go ahead and send another test email and it should almost be instantaneous.
Once you have verified this, go ahead and delete the email messages you sent from the iPhone. If you are logged into http://www.me.com, please sign out while you delete the email messages on the iPhone. You should then log back in to see if the email messages are still there.
Im trying it now i'll let you all know if it works....
And then put your hand on your head, turn around twice counter clockwise and flush your toliet. Should be good...