I've been using them since late September.
They really rocked when they just started, high CTR and very high EPCs. I earned a huge amount of money from them in the first 5-6 weeks but I knew it couldn't last because I couldn't imagine that advertisers were making a good profit. So after a while Chitika received complaints from the advertisers and they made some changes to the ads to lower the CTR. The advertisers were still probably not satisfied and they started lowering their CPCs. The lower CTR and lower EPC resulted in six times lower earnings so I decided to remove them on some of my sites and pages.
They pay on time and they still bring in about $500-600 a month but the performance of Chitika isn't as good as when they just started.