I agree with xboxundone. There is a lot of money to be made out there but not everyone can come up with the great ideas or have all that start up money. And people sometimes do flip flop between affiliate and merchant, also some people do both.
If you want to maximize the profit for doing a minimal amount of work, find a two-tier affiliate network so you can make a profit from the others you recruit, as was mentioned before.
Lastly, don't put all your eggs in one basket. Use different networks, run different campaigns, and never stop learning what's out there and what's hot. You'll find what works for you, which may change over time, but that's what you stick with. And it does work :)