CloudFlare also caused huge performance issues on a side project which I didn't notice until recently. I was consistently getting 1.2s+ responses on a couple of pages, and 600ms on a completely static page.
So, not only did CloudFlare not help on the pages that were truly static, it was actually making everything worse across the board. Hitting the same site with my direct.* DNS cut from 1.2s+ to under 500ms.
CopperEgg and others also kept reporting that my site was down or otherwise super slow when on CloudFlare. I'm not sure if this is because of throttling or something else that might have been in place with the CF service, but either way I was often unable to reproduce the "down"/"more than 6s" that CopperEgg kept reporting.
In short, I think CloudFlare's services sound good in theory, but I'm not sure they have figure out all the issues with scaling and performance yet. So, I cut them out... and certainly not going to be paying any time soon.