I have seen many posts about Chitika here in Webmasterworld.com and I had to see what the talk was all about so I applied an account and I was just approved less than a week ago.
Since then, I have tried many different positions for the ADS - color variations, etc.
I have then concluded that Chitika is a great compliment for Adsense. The way to make the most out of Chitika is by placing it, with specific products, in pages where Adsense is either not delivering good targetting or poor-paying keywords.
I built a history-related website almost a year ago. With Adsense, I would hardly make five cents per click. Even though Adsense had a much higher CTR, products in Chitika would pay me up to 50 cents per click! This meant that I kept more traffic and I earned more money. I, of course, left Adsense in some pages - but Chitika did help greatly the less-targetted ones.
I therefore conclude that Chitika can be much better than Adsense if placed correctly in a page. For example, placing chitika in a SEO-related website will make you pennies - but placing Chitika in a website in which a specific product can be sold is almost always better than Adsense.
For this reason, Chitika should be looked more as a compliment for Adsense and not just a separate product per se. Even though the Adsense TOS doesn't allow the competition ADS in the same page, one can still place them in a different one - which is what I did to maximize my revenue.
Those are just my experiences, and I'd like to see what everyone else thinks about it - and if you have tried it.