Powerlevelling question.

[Lazortag]

So for all of you monks and druids out there (am I missing a class?) who power-level people for money, how many levels do they gain after an hour? What about after two hours? When does it start to become extremely unprofitable? Basically, if I were to PL someone on one of my characters, how long should it take me to get them to certain levels (assuming I'm being fairly efficient, going to the right zones, pulling fast enough, etc.)