I use CloudFlare for caching and security purposes but I just use the free plan. The free plan is awesome and I think everyone should use it. You don't even need to use CloudFlare as a CDN, but you can use it as a central place to manage DNS for all of your registered domain names.
CloudFlare acts as a reverse proxy for your website, according to the post on the CloudFlare blog that is available at http://blog.cloudflare.com/top-tips-for-new-cloudflare-users. They even have a WordPress plugin to make capturing visitors' real IP addresses easy and to tap into Akismet for not allowing known spammers to load your site. If you're interested in more about CloudFlare, I suggest reading this post from the CloudFlare blog as well. It even mentions WordPress integration.
CloudFlare gives really cool stats too; see an example in the following screenshot:
I have to suggest that everyone use the Jetpack plugin from Automattic as well. With that plugin, there is...