This is actually doable. There's a tweak to PageRank you can do (that's as old as the original paper[1]) that allows you to bias the ranking toward a certain set of websites. It works really well.

While it's probably unfeasible (or at least really expensive) to do completely personalized rankings, that's just too much data, but segmenting off into areas like academia, blogosphere, tech, etc. is quite doable, and as the authors remark, this approach is highly resilient to manipulation from commercial interests.

[1] http://ilpubs.stanford.edu:8090/422/1/1999-66.pdf