I got 1 OEM and 3 generic's and never had any problems for my Canon 20D

 

I bought 3 Digi Power batteries for my Nikon D300 when Circuit City was closing for $10 a piece they've been holding a charge just fine and seem to last as long as the OEM battery.

 

I have 2 aftermarket batteries (CTA I believe) and not only are they IMHO the same quality as OEM, they last 30% longer. Maybe I'm lucky, maybe not, but I got them both for $10 each on overstock. For insurance purposes, I use them in my grip, that way, if anything happens, I lose the grip, not the camera.