When I bought my SX10IS a couple years ago, I was really excited that I was getting a camera with AA batteries: a set of spare rechargeable batteries would be pretty cheap, and in a crunch I could buy another set at any corner convenience store. But once I started using it, I learned a little more:
- AA batteries are heavier than proprietary Lithium-Ion battery packs.
- AA batteries, especially rechargeables, have a shorter life than the proprietary battery packs.
- NiMh (most rechargeables are NiMh) and Alkaline batteries don't do well (only last a few minutes) at cold temperatures (roughly freezing, or a few degrees above).
- Lithium (i.e. work-well-in-cold-weather) AA batteries are expensive compared to NiMh or Alkalines.
- One spare proprietary battery won't cost too much more than a charger and two sets of rechargeable batteries.
- A set of AA batteries don't last for as many shots as a proprietary battery pack (rough guess: they last about 2/3 as long. I've never tried any sort of experiment, that's really just a gut feel).
So I know it seems wrong, but a proprietary LiIon battery pack is actually better than AA batteries (especially if you live somewhere that gets down to freezing temps in the winter).
(And on the Canon vs. Fuji front: I really enjoyed shooting with my SX10IS. I can only imagine that the SX30IS is an improvement over it. And if you're into hacking on your camera at all, CHDK will give you some added benefits, like scripting.)