I've started trying CloudFlare as a CDN for my web site. They have a nice free plan that works well for personal and smaller sites. So far it seems to be going well. Not that I was having any problems with my hosting, but it's a fun thing to try. And it's nice to have some security in knowing that my site won't blow up if I accidentally post something wildly popular and get Slashdotted. And in the case of a server failure, as happened yesterday, my site is still (somewhat) accessible.
As a brief description of how CloudFlare works, you host your site as normal, and visitors will connect to CloudFlare's servers rather than your own. If CloudFlare has a cached version of your page (that is still current), then the visitor gets sent the cached copy; otherwise it queries your server for the contents.
One nice thing about CloudFlare is that it includes IPv6 support, even in the free plan, which is great for when your host doesn't have IPv6 support. Of course, I still don't have IPv6 ssh, email or Jabber, but it's a start.
CloudFlare also doesn't charge for bandwidth. If your site gets Slashdotted, you don't have to worry about increased charges (at least, not from CloudFlare — you might still exceed your host's bandwidth allowance). You just pay your plan's rates (or not pay, in the case of the free plan).
Redundancy. I'll say it again: redundancy. If my host should ever become unavailable for whatever reason (yesterday, it was hardware failure), my site (at least whatever CloudFlare has cached) is still accessible. If CloudFlare ever goes down for an extended period of time, I can change the DNS records so that visitors go directly to my server. (Of course, due to propagation delays, that would have to be quite an extended CloudFlare outage.)
CloudFlare is also a very transparent company. They had a network failure not too long ago, and they were very upfront about what happened. No matter what you do, something will always go wrong at some point. It's how you react to things going wrong that differentiate companies. Even when things don't go wrong, CloudFlare shares a lot of their technical details on their blog.
Unfortunately, there are some limitations. CloudFlare takes over your DNS service. This is necessary for how CloudFlare operates: they must be able to return different DNS responses depending on the visitor's location. But this means that you must use CloudFlare's DNS editing interface, which isn't as flexible as editing a zone file by hand. I had to give up my CSA and RP records. Given that almost nobody uses CSA, and my contact information is easily found on my site, it isn't a great loss.
Another limitation is that the free plans doesn't include SSL support. This is perfectly reasonable, given that it's a free plan — you need to give people a reason to pay. But it's something to be aware of. I only really needed SSL for my OpenID service, so I just put it on a different host name, and set it to not be handled by CloudFlare.
CloudFlare is a very popular CDN, which means that if it should ever go down, it would take down a lot of sites. It would also be a popular target for attack. As more sites use CloudFlare, it's becoming an Internet monoculture. So if anyone knows of a similar service, let me know and I'll give it a try.
All in all, CloudFlare seems like a good service, and the price is right. I'll keep it on trial for a bit longer, but it seems like I'll be keeping it.