Very nice DNS management, faster page loads, reduced bandwidth usage and server load, and all of the nice security features (blocking malicious clients, XSS protection, etc). And all of it with practically no configuration and it's free unless you need SSL (and/or more advanced security features).

Also, they pass along a country header which comes in handy if you need to know which country a user is in without having to set up GeoIP and keep it up to date.

Oh plus they sent me a t-shirt.