arronsky - 12:41 am on Jun 25, 2010 (gmt 0)
Fantastic post and advice from Tedster. You have to both have cookies cleared PLUS opt out of customization each browser session to avoid getting personalized results. Even then, I believe Google will customize to your hour, location, and whatever else it knows about you (browser, screen resolution, etc... could you imagine if it decided to show 'simpler' results to people with 640x480 screens? haha).
4, 5, and 6 are incredibly important points (particularly #6, that's a genius observation that I hadn't really considered much but is definitely happening).
One other thing I'd add is that many searches are now auto-corrected by Google, e.g., search for chomocolate and it will show you chocolate results, telling you that you can switch to the chomocolate results if you like. Don't quote me, but I BELIEVE this behavior used to be exactly the opposite, only suggesting the other search but showing you what you searched for. For people who got traffic on obscure or misspelled/mistyped traffic, you can rank #1 and only get 10% of your old traffic.