I've seem some oil analysis' on VWvortex where they were doing some sort of scientific breakdown on synthetic oil at 10k mile intervals (if I recall correctly) and it was still fine at 30k miles... It's been quite some time since I've seen it, so I'm not sure if my figures are completely accurate, but it was a pretty interesting read. I'll have to see if I can still dig it up.

I don't know that I would change it every 30k miles just because someone says I can, but I know I sure would like to see some sort of MythBusters episode on the topic