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There are some programs that this approach works for, as well as there are many more where this won't be profitable.
Unless any of the parties have something against this method, it only takes time and money to see if this approach works for you.
Although the downside is having to track extremely closely your conversion rates. you obviously don't want to spend an arm and a leg and have no return for it.
you have to choose keywords that you know will convert well.
But I have also found that some affiliate programs don't like affiliates with no website. And I have also found that Overture will not allow any sites to link directly to affiliate sites with tracking code in the URL if they can help it.
However, on the smaller PPC engines, where I only had to pay $0.01 per keyword, it seemed to really pay off.