Camcorders that run on 3 AAA bateries, how long do the batteries last????

I assume we're not discussing the Sony DSC-W55 since that doesn't use AAA batteries.
The battery life varies depending both on the camcorder and the type of batteries. In general, lithiums will last longer than alkalines, which will last longer than a single charge on NiMHs. On cameras that give you the option, you'll use less juice shutting off the display and using the viewfinder. Many manuals will give you estimates of battery life, but these are estimates only, the battery life also depends on how YOU use your camcorder.