There is a long string on it here somewhere. (I know because I started it a few months ago.) I argued about the need and learned that many of the old timers (whose opinions I respect) seem to pull their batteries daily. That said, I seldom have on any of my BBs and as MD says, recommend to just do it when you encounter a problem. If you seem to have frequent problems, then you may want to get in the habit of just doing it regularly (daily) before the problems occur.
Personal: iPhone on AT&T
Work: BB 9650 on Sprint
I do it whenever I'm bored..
Or once a week..
Or when my file free goes below 20mb..
Or when I remember..
I was one of those people with an 8100 though and got in the habit of doing so every other day. Here again recently I've been doing so almost daily on my storm because I've been playing with apps a lot... Check your file free status, and do it whenever it gets low?
Storm2 has been incredibly stable and probably doesn't need frequent pulls. Nonetheless, I downloaded Quick Pull from the App Store. It does a "pull" on schedule every 24 hours, and the device works flawlessly.