If you're part of the club that wanted Google mail pushed onto your iPhone, the release of the GPush application did sound like good news. Unfortunately the application hasn't worked that well after its release and people started to complain. I was one of them: in this blog and directly to Tiverias Apps.
It was probably a scalability problem: they never tested an application with such a great number of users and GPush wasn't exactly the kind of application that passes unobserved. We were waiting for it! On its website support page Tiverias Apps has been constantly giving feedback to the users about the problems that we were experiencing. Finally I'm glad to state the following: GPush is working flawlessly for me since a couple of days.
There's some glitch, still, but I'm confident they will be resolved in a GPush application update. Specifically, I still can't change my account settings without uninstalling and reinstalling the application. It just ignores the change.
It was worth what I paid for it.
Update: You don't need GPush anymore if you want to have your google mail pushed to your iPhone.