BTDT, in my iPad under 4.3 and MobileMe... I have an Executive level case on the problem, they see push get turned off on my iPad, then turn itself back on, BUT, everyone on the iOS team that needed to be involved was busy working on the iCloud and iOS5 launch.... I'm talking 4 plus weeks of emailing them logs of it happening.
Turning the device on and off resets it for a few days.
I suggest logging a call with apple on it - maybe my logs are finally in the hands of the person can solve the problem and it can get fixed, because from what I'm hearing the problem hasn't gone away (and I haven't updated my iPad to 5, nor my MobileMe account to iCloud).
Good luck, and be sure to get it noted.....