OK, so some people pointed out that it could be targetted advertising. See, as far as I can tell, that'd mean they've gotten a grand total of two ads targetted at me properly now. The rest are for things I have no interest in, so I'm not sure it actually is targetted advertising. Anyway, here's the other Linux ad I saw on Facebook:
Yes, it's Ubuntu this time. Last time, it was Fedora 9 on a USB stick.