I'm set up with Gmail push via Nokia Messaging. Works OK in general - the push is much more convenient than polling if you use email heavily, and the killer benefit is scheduling times when it DOESN'T sync - so you don't get woken up overnight with email arrival alerts, but they kick in again just after your n900's alarm wakes you (to the sound of "I'm only sleeping " by the Beatles ... lovely, it should be the default alarm IMO).

But there is a definite issue - for me anyway - whereby push seems to stop working at or some time after you leave home wifi coverage and go mobile on GPRS. I have messed around with this and empirically, I think that immediately after leaving wifi. if you do a "send & receive" it seems to kick the push back into life?