If indeed Google did lose out on buying StumbleUpon to eBay, they’re moving quickly to prove they can simply build it themselves.
They’ve just announced their own random search button to the Google Toolbar. Adding the “pair of dice” to your Google Toolbar will allow you to randomly surf web sites that match your interests, based on your Google search history (you have to enable Google search history).
OK, so it doesn’t have the same social networking aspects that StumbleUpon has, but it certainly has a larger index of sites to pull from.
In StumbleUpon’s favor is that the new feature is very limited and you have to enable it, to use it. That said, like anything that Google rolls out, if it becomes popular, look for it to be added to the default experience.
If you don’t like the whole toolbar random deal, Google’s also introduced something similar as a tab on Google Personalized homepage.