Is it normal for push notifications to sometimes not work?
I've had this problem with hactivated 4.3.3 iP4 with SAM so I restored and activated with AT&T sim and it's still doing it.
It was working fine for an hour then I tested it with iPusher and it kept saying "Please wait" and then around 5 minutes later it said push notifications work fine...
Many things can interfere with push. The originator, Apple, your carrier, the data path, your device. Usually they're good, but push is like SMS - not guaranteed delivery.