Why I use Cloudflare
CloudFlare's line of security features are also impressive. They do analysis of traffic heading too and from the server watching for malicious activity like XSS and SQL injections. When CloudFlare detects users doing this over and over they get blocked from all CloudFlare enabled sites. Rules can also be written to restrict content on a user level or even country level.
My favorite part probably because I am a networking geek is the use of anycast to route traffic. So even though my server is in Rochester I get good latency because it is mirrored in San Jose. This is normally a feature only available to companies with dozens of data centers spread across the country.
These are some pretty impressive features for a free service. I would recommend this to just about every webmaster out there.