What's considered a slow miner
Everyone has different opinions on that, but I would say that Slush's pool would probably be beneficial to anyone getting >100mhash/s.
I know that's still low, but some people like to help the network (every little helps), or are just testing (CPU miners etc).
Anything <100mhash/s would get better and more consistent/stable rewards from a PPS site like 50BTC.
K.