Not that this is necessarily new information for the SEOs of the world, but for those who might be newer to the world of search engine optimization, it's always fun to pass along information that comes straight from a Google employee's mouth. (Which isn't to say you should believe everything a Google employee says, but it's usually fairly obvious when their tongue ISN'T forked. hehe).
Today's tidbit comes from an old friend of many SEO's, John Mueller (johnmu or formerly known as softplus before Google absorbed him into their fold). John gives a quick answer to a question asked by niemi over on the Cre8asite forums. niemi wanted to know if it was true that two people could get different results for the same search based on their surfing habits. John's reply:
There are all kinds of personalization that play a role in Google's search results.
So there you have it, straight from the horse's mouth. (No offense meant, John).
Run on over to the thread if you want more details.