On one hand I'm really enthusiastic to see attack mitigation tech like that becoming available for more people, but on the other hand I'm worried that this is just another step in centralization of The Internet. We've seen CloudFlare change their policy once and shut down a controversial website, and if they're one of the only people able to keep services online in an attack-ridden web, that gives them far too much power.
Not to mention the already-present breakage of the SSL "contract" by CloudFlare running a MITM proxy on secure webpages.