I was alerted by Todd and Kaede that the Rubenerd Show RSS podcast feed thingy wasn't working properly for them. I had a look on my server and it turns out the RSS feed php file was corrupted when I upgraded to the latest version of WordPress last night. As far as I can tell that was the only file affected, but to play it safe I re-uploaded every server-side file again.

Hope that clears it up for people, sorry for the trouble.