Will most USB PS2-like controllers work on PS3

In Windows it works out of the box, but if you install this software the Xbox 360 will display a battery indicator on the screen.

In Ubuntu, the Xbox 360 controller works flawlessly with xpad. (I've tried this successfully with a wireless controller)

In Mac, I've found a driver here, but I haven't tried it because I don't own a Mac myself.

The Sony DUALSHOCK 3 controller requires a USB handshake with the AC adapter before accepting any connection. If your wall-plug charger contains the circuitry required to negotiate the handshake, then it should work provided it can supply the minimum amount of current.

So in other words, you need a charger built specifically for the PS3 controllers, or else be able to negotiate a handshake with a PS3 controller.