Google has announced that they are offering a StumbleUpon type of service. Google Offers "Queryless Search" & Personalized Recommendations from Chris Sherman at Search Engine Land explains it well. In short, Google uses your search history to determine which sites you like and then if you click on the "recommendations button" in the Google button, it will take you to one of those sites, randomly.
We'll give you up to 50 new sites per day that might be of interest. Just add the button to your Toolbar. (In order to use this feature, you need the latest version of the Toolbar.)
I installed it on my Firefox browser on my Mac, and the button looks like a pair of dice. Here is a screen capture:
There is also another feature they launched that "allows you to add a "recommendations" tab to a Google personalized home page. To enable the feature, simply add a new tab, name it "recommendations" and tick the "I'm feeling lucky - automatically add stuff based on the tab name" checkbox." But honestly, I think this was available in the past.