Sure, it's valid. That's why it'll be important to manage your affiliates and not let them go nuts. (And boy, they will.) Fortunately, you can go far by having

Sure, it's valid. That's why it'll be important to manage your affiliates and not let them go nuts. (And boy, they will.) Fortunately, you can go far by having someone look through the referrers and see who is playing games and nuking them. As to an affiliate system, you need to figure out what are essential features. For instance, do you want to cut checks? Do you want it to be multilevel? Do you want to be able to modify the source? (And what language do you prefer?) What about budget? All critical questions you'll want to ask before you start the hunt.