What would you add to this used car buying checklist?

If you've bought a used car before, what would you add to this checklist?

I've been putting together a used car buying checklist after reading advice from mechanics, forums, and experienced owners.

Before I call it "complete", I'd love some feedback from people who've actually bought or inspected used cars.

What are the biggest things people forget to check?

Any expensive mistakes you've learned from that should be on the list?