Pageback is a website mirroring service that makes a copy of your website and hosts it on a CDN (Amazon CloudFront + S3) so that it is always available. You can flip to this backup site during an outage or while undergoing maintenance.
Here is a demo mirror site for Hacker News: hn.getpageback.com
Pageback is now in private beta and I am looking for more folks to try it out. Thanks!