I suspect it's very much the same as with the faucets themselves, big traffic = big money, low traffic = low income.
So, it all depends on how good you are at drawing traffic.
Myself, I'm much better at coding than I am at marketing, layout and graphics = lots of work for very little payoff. If you're the other way around you should be able to make it worth your while. I guess the work is it's own reward in my case.