The number of accounts / buddies will affect battery life - the more updates you recieve for accounts & buddies (status changes, etc) the more radio usage there is, and the more battery is used. The 3G radio uses more power than the Edge radio, so you'll see more battery drain with the bold / storm / tour.
That being said, we're implementing changes to reduce radio usage while the app is active & idle. These changes will be in the next Storm beta & in the 2.0 version for all BB models with OS 4.2.1 & up.
I'm hoping to get the next Storm beta out next week...
