I have to agree that the proprietary battery pack is a drawback on the Canon G10. However, my experience with rechargeable batteries in the past 3-4 years, the G10's battery (NB7L) specs and reports regarding the G10's battery working capacity (approx 400 shots per charge) lead me to conclude this should not be a deal killer. I would certainly get at least one, and be inclined to get two backup batteries.
While Lion (lithium ion, rechargeable) batteries work well they are rather expensive. They basically decay in several years whether you use them or not*. (So don't buy one and save it for later.) Will they still be available in 10 (or whatever) years? Will I have to discard a perfectly good camera because I can't get a new battery?
Lion cells are also rather delicate--full discharges will significantly reduce their lifetime. Overcharging and reversing cells will destroy them.
* Store Lion batts at 40% charge 0C (32F) to maximize their functional lifespan.
http://www.batteryuniversity.com/parttwo-34.htm
I read somewhere that cellphone** manufacturers refused to consider standard sizes for Lion batteries... (Standard sizes reduce cost and improve long term availability. Consider, for instance, the availability and costs of AAA, AA, C, and D cells.) It looks to me like camera manufacturers are doing the same thing. Even worse, a number of devices (eg iPods) come with non-user-replacable Lion batteries...
** Most modern cellphones use Lion batteries.
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Maybe I'm old fashioned, but I favor cameras with standard battery types (eg AA), 28mm lenses (for scenic photography), and viewfinders (for bright environments and it is easier to hold a camera steady against your face than just out in your hands).
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Doug