Another thread I was looking at reminded me of this, but then I realized the thread was 2 years old and is about only a subset of what Cloudflare does. Have you heard of Cloudflare? Anyone considered using it?
The intriguing thing about it is the uptime guarantee, and protection from spam and various other "bad" visitors. The plans page has the feature list.
The main worry is that it could block wrong visitors, cause delay in page updates (like with caching), and change some URLs to point to a CDN (I'm not sure if it does, or how would it work if it kept all URLs exactly the same).