I have just found what could be a major pitfall of it, though. I configure my profile, then I search for "diego vega". When I move the personalization slide to the max, my own blog jumps from the first place to the last one in the first results page. The link doesn't even have the color balls on its side.
Then, if I write about what interests me more, how can you explain that my blog gets so poorly ranked by the application of my own preferences?
If anybody from Google is listening: Give me a "personalize by example" option. You want a sample of what I really care about? I will tell you: http://diegov.blogspot.com
[Deep guessing in the abyss of my mind: They are probably matching each page against a predefined (and probably human made) category tree. And my blog hasn't been categorized at all]