If you're referring to the "Always on mobile data" feature, I have it unchecked and my GMAIL pushes fine... This feature only affects you if you're not in Verizon's area of coverage. A post a while back said it's for use when you go into an area where Verizon leases like Alltel's towers and such. So, if you're in a good Verizon coverage area, uncheck it and save some battery.
The feature you may be thinking of is in the "Accounts and Sync" area that allows you to check or uncheck enable background data. That would disable a GMAIL push...
IMHO, this is not 100% accurate in all situations. I use Exchange. I unchecked "always on mobile data" and noticed a minor, but annoying, issue. Only some of my mail would "push" through to the phone.
If the phone was sleeping and I wanted to check my mail, upon waking the phone and hitting the mailbox, I would get a message that the connection failed and asking me to connect to mobile data or wifi. After cancelling this message, my mail would immediately load. Clearly, that is not true push. And clearly, this is not how the Exchange should work. If gmail works fine, so be it. But this is my experience.
I was not willing to deal with this admittedly minor issue. I have since enabled "always on mobile data" and truthfully, have not noticed any change in battery life at all.
I'm on day 1.5 of the 1750 battery. I've been off the charger for 5 hours. I'm at 90% battery remaining. I plug in every night. Even with my curve, my Storm 1, and my Tour, I plugged in every night. No big deal so long as I get through the day.