Done right, any website can benefit from pay-for-performance. Here, however are three types of websites that benefit tremendously from well implemented commission-based sales.
Product Reviews -- When people try to find product reviews they are already seriously considering purchase. If you review DVDs, books, software, or just about anything where your opinion matters, immediately after reading a positive review individuals are highly likely to purchase. Be careful, however. Websites to only publish positive reviews are held skeptical by readers. Your positive reviews will generate far more sales if the mixed among negative reviews. Another strategy is to combine a positive and negative review. "I hated the movie, but my girlfriend cried... and for some reason this is a good thing." People who identify with your girlfriend more than you, are likely to buy this movie in spite of your negative review.
Personal Blogs -- Generally speaking, I am against personal blogs. They tend to be rambling and unfocused. However, some blogs generate a strong core of loyal readers. These loyal readers check back every day, leave lots of comments, and feel like they have a personal relationship with the blogger. These readers are strongly influenced by the recommendation of an "friend". This website is ripe for pay-for-performance. My personal blog generates reasonable revenue in this manner. I signed up for Netflix, and published a referral link and made good money. If I recommend a book, people buy it. My personal blog, www.sunfyre.com will never make me rich, but every dollar counts.
Expert Endorsement -- The blog you're reading right now is a good example of an expert endorsement website. If you want to learn about website marketing, and I've been successful at establishing my expertise, if I recommend or endorse a product you are far more likely to buy it. The expert endorsement strategy only works, however, when the product being endorsed is targeted toward users. I'm not going to be able to recommend a good movie with the same impact as the personal blogger, unless that movie happens to be about website marketing.
As we've discovered, with all three examples, the reviewers credibility is absolutely critical. You can establish credibility through objectivity (product reviews), reader/writer loyalty (personal blogs), or expertise.