I've seen accurately targeted technical ads when viewing my local paper's site that are creepy as well, since there's "no way" they should have known enough to put that ad there, and was musing on a post about this creepiness, too. Recommendation engines are interesting, and it is amazing how much information can be gleaned from simple yes/no/didclick kind of stuff, but it can also reach a creepy point faster than we might think. Sort of like the little "20 questions" novelty toy that can surprise you, where (I assume) it exploits the effectiveness of dividing the solution space in half with each question... you do that 20 times and you've reduced the space by a factor of a million.