Ask HN: Cheap laptop for Rails web development?

Recently I've found that working on projects from home on my desktop is just killing my productivity.

I'm looking for a laptop competent enough to do Rails, but not much past that - I don't need to be able to watch HD video or anything. Something that will be compatible with Ubuntu.

I've read that you can request a refund from Microsoft if you buy a laptop with Windows 7 and decide not to use it. Is that true?

I'm looking at spending under $400. Any recommendations?