Affiliate programmes will generally generate more revenue than PPC. Think of PPC as an annuity system for affiliate programmes with a middleman taking their cut.
Lets say I have a $50 product being sold off a landing page that converts at 1:100. I offer you $10 per conversion you send me. If you send me 10,000 clicks there will be 100 conversions and I will pay you $1,000. My budget for 10,000 clicks is therefore $1,000, or $0.10/click
So I go to a PPC service and ask them to pimp my affiliate programme. I pay them $0.10/click. They put my ad on your site and pay you 50% of revenue. You send me 10,000 click and you make $500.
There are reasons to use PPC though. First and foremost, it's easy. You just stick an iframe into your site, or park your site on their server. In the last case you don't even need a site, a server, anything. The second is probably aggregated billing. You get a single cheque for all your clicks regardless of where they went.
Affiliate programmes on the other hand, require a lot of work. You have to find them, join them. Design a site, host it, put all the links in, etc. Some sites use a payment processor that will aggregate payments from all your affiliate programmes. Some people will pay you with paypal. In the end you will probably end up getting a dozen cheques each month instead of one. If you get charged for depositing a US$ cheque then you have to deal with this added cost. You also have to increase your minimum payout on each affiliate programme to something that allows you to earn a living instead of just working for the bank.
So if your willing to do the extra work you will make more money. I run affiliate ads right along side Adbrite ones on several of my sites. Adbrite is a great service, and only takes a 25% cut. Even so my affiliate revenue still beats my Adbrite revenue by a good margin.
