When you turn a PS3 off, it also disconnects the power to the USB ports. This makes me wonder why Sony built the controllers to charge over USB if you can’t charge them with the PS3 off.
Personally I always figured the point of having a wireless controller was so I wouldn’t have to plug it into the system when I was playing. I’m also not comfortable leaving the PS3 on when I’m not playing it.
Luckily Nyko came out with a product for just such an issue. They have the Dual Charger AC, a very simple plug for the wall that provides two USB power sources. It even comes with two USB to mini USB plugs. So just plug it into the wall and then plug in the controller. Very simple, very well built. Since the controllers are just USB, the dual charger charges them just like the original PS3. Not much more can be said about it, it is simple and does what it was designed to do and does it well.
The Dual Charger could also be used to charge any other device that powers itself off USB. So I give it a 10 out of 10 — nothing lacking on Nyko’s part.