I'm using ymail to get "push for gmail" and it works perfectly. It might almost be better since I setup filters to only forward email I want to know about immediately to ymail. At this point I don't know if I would use gmail for push directly if it became available because of this filter technique I'm using. One advantage I have is that I don't need any contacts or calendar from gmail since that is all done with my exchange account.
Here is a blog of what I did in more detail if you are interested:
When Will Apple? » my iPhone gmail push work around…thanks ymail!