Seriously, if you ONLY use if for occasionally phone calls, you won't have a battery issue. If you flick through the screens, reading news widgets and checking facebook/twitter for a few hours, then you will drain the battery. Just having the phone in your pocket won't drain the battery significantly. The hard part is not taking it out and fooling with it.
I am running CM7 (Gingerbread) on my Incredible and see significant battery life improvements. It's hard to say how much is 2.3 and how much is Cyanogen modifications.