My tub faucet's been leaking constantly and I have no idea what's wrong. It even leaks when I turned off the water to the house and when I take the cartridge off (it doesn't leak if I leave the cartridge in place though).
It's a single lever handle.
Here are some pics:
http://img17.imageshack.us/img17/8470/img4664s.jpg
http://img40.imageshack.us/img40/2826/img5360g.jpg