I've been running the mobileme free trial since Sunday Night and is working great no problems at all. However this is a new connection not an upgraded .Mac, which seemed to be where the main problem was.
I am getting mail updates quickly, even from my Web Mail out to the Internet, then OTA to my phone, so I can actually see how long taking.
However I will be using the family pack so works out lot cheaper as using multiple accounts.
If just want push mail then look at Yahoo as apparently does Push Mail, then just synch via iTunes on your PC/Mac at home for the Calendar.