While I don’t get all the technical talk, the gist of this article at SEOmoz is that, as I’ve said before, the Google bot is a very good reader. I ran the LDA tool (Latent Dirichlet Allocation, or topic modeling) on Supak.com for “free desktop wallpaper” and got a 32%. Made a few changes, ran it again, and got a 55%. The changes? I added this paragraph under the right hand link to the computer backgrounds blog:
Download all kinds of free desktop wallpaper, including high resolution nature photographs, abstract photography, winter wallpaper scenes, cityscapes, and more!
So, be a good writer and the Google Bot will reward you. My suspicion is that adjectives, adverbs, and the like are extremely important here. Also, using your keyword’s multiple forms (verb, noun, etc) is helpful.