A WebmasterWorld member points out that Google has been a little more open with regards to personalized search results. For example, when you do a search, you might see something like this, where Google says that these are searches based on your web history:
When you click on "More details," Google gives you more information about personalization:
Google announced this transparency at the end of July, and it's been relatively welcome addition. They fear that the results could still be personalized if you're not logged into your account, however.
On a similar note, Pierre Far has written that you can now opt out of this behavioral tracking, and he directs you to the forms you need to fill out on Google and Yahoo (in addition to NAI).