A stumbled accross a TED talk tonight by Eli Pariser, Author of The Filter Bubble: What the Internet is Hiding From You. It covers some personalisation and censorship issues on the web, primarily talking about Facebook and Google customising feeds and search results with the end user having any control.
The video specifically mentions that Eli was told, "by a Google Engineer", that the search giant uses 57 individual signals to personalise the search results, despite the user not being logged in. Eli goes on to give a few basic examples of how search result pages differ massively based on this personalisation.
Watch the video below: