I use 4 AA NiMH batteries in my camera (a Canon S1). I have some 2500 mAh energizer batteries that I will not use in it and I have some 1800 mAh sanyo ones that I use regularly. Why? because of variances in the batteries and their self discharge rate.
When my wife wants to take a picture of the kids doing something cute we need the either the batteries in the camera to not be discharged, or for there to be a charged set of batteries ready to go.
So I bought a bunch of 2500mAh batteries thinking these would be a good thing. but they didn't seem to last as long when shooting and they were often discharged after sitting for a while. I found out a couple of things, the first is that after using these batteries for a while I would end up with one cell that was discharged more than the others. This was enough for the camera to say that I had low batteries. The other thing was that if I charged up a set of these batteries, a week later the wouldn't have enough charge to run the camera. These batteries had a very high self discharge rate.
So at the end of it, its no good to have high advertised capacity if its not going to be there you
I have had good luck with sanyo batteries. The new sanyo eneloops have a low enough self discharge rate that out of the package they have a usable charge