Same here - have had a lot of mails in the past few days that weren't "pushed" to my iPhone - had to go into the mail app for them to come through. Seems like MobileMe might be experiencing some problems? Or we having network issues?
Mine actually came right in the last few days - seems fine now
Figured out the entire reason for my delayed push email issues. Wifi on and phone is asleep I don't get my push email until I unlock the device. I turn my wifi off and let it go to sleep..send my self an email and it pushes perfectly. I've been trying this repeatedly and i get my push mobileme mail without fail as long as my wifi is off.
I'm happy to have my push working flawlessly again, but mad at not being able to use wifi unless I can use the below DNS settings and get it working.
WIFI:
Apple - Support - Discussions - Push Notification Doesn't Work When ...