I've always wondered if Google doesn't give a small boost to validated code - if I were them, I'd want to encourage things that make life easier. (Another example of them doing this is them penalizing low slow times - I really don't think an extra 5 second loading time effects 'the user experience' to the same level it affects the 'Googlebot resource allocation teams experience')
I've got one client who is punching way above his sites weight, and as much as I'd like to take credit for it, I think his social strategy (Which he's doing in house, mainly Twitter and Facebook) is what's actually giving him the push. I, of course, haven't told him that. :)
Google is, at the moment, really sensitive to anchor text abuse. If you are looking to make a quick buck, that's the way I'd go about doing it. As ever with blackhat, that loophole will be closed pretty sharpish. If your going to flog a crappy Ebook, now's the time!
If your like my clients and have generally narrow business focus, having keyword heavy domains is working a treat for me at the moment.