I guess from a professional standpoint, I never wanted to run out of juice on a location shoot. You can never have enough videotape, film (sic) or battery power, and flexibility is King.
I recommend the same thing to consumers, because for MOST of their cameras, a day in Disney World would cause real problems in battery power (and memory as well). I usually carry 3-5 sets of rechargeable AAs, but know that I'd have to be pretty far from a convenience store to not get back-up if needed in a pinch.
It's not a deal-breaker to me if a camera has a proprietary battery setup, but all other things being equal, I'd choose a model that took AAs if I had to choose.
