1) Response times, in general, are terrible with Cloudflare enabled. This chart [http://goo.gl/JX1v6] shows how Googlebot responds when cloudflare is enabled and disabled. With Cloudflare enabled in June, response times are above 1000ms. I have since disabled it in the middle of June and response times returned to normal.
2) Cloudflare is getting worse. Look at the chart again. Notice the elevated response times in April? I also had cloudflare enabled then. They hit around 400 - 500 ms in response time. Then I disabled it again at the first of May.
3) Ajax requests, most notably, POST have increased noticeable latency. Some days are better than others.
I do not have anything "special" enabled. Minimize HTML,JS, CSS are not enabled. Nor is rocket loader.
I'd also like to add that when "cache everything" + Minimize HTML, JS, CSS + Rocketloader is enabled, then response times seem to be perfectly normal on a different site hosted on the same box. Googlebot: [http://goo.gl/DRDnF]. However, most of us cannot use this feature unless our content is static.
Everything posted here is based off a free account. I will also be cross-posting this on the cloudflare blog post that this links to.