If there's one thing that's made me borderline OCD (happy now Michael ?) would be the world of personalized search. Probably more so, behavioural data, is an area (both explicit and implicit) that seems to be part of any likely evolution of search engines (and by extension SEO). Now, I am not alone in this. The folks at Google have also been more than a little motivated as well. Or as Marissa Mayer said a while back,