After I updated my Stumbleupon tool bar this is what I saw after I used Google.

As you can clearly see, where someone has stumbled a web page, or given it a review a variety of little icons are placed next to the results.

Hover over them and you see that a click will take you to a stumbleupon page for that website.
At first I was pissed off that Stumbleupon would just do this without asking or telling me, but then I thought, this is really clever.
I could do some interesting stuff with this, I can now see what doesn’t get stumbled and what does. I can find people who are interested in specific verticals a lot more easier than using the stumbleupon toolbar. I can then contact them and ask them for things like links.
Now if only the Google serps could be re-ranked taking the stumbleupon traffic into account.
What if Google buys stumbleupon and merges with the Google toolbar, hmmm, how useful will a stumble be then.
My advice, start a Stumbleupon account and get stumbling your own stuff before someone else does. I have already claimed the Wikipedia Shoe page ( I’m not a shoe nut, but I thought it would be funny ). I was going to claim Cadbury.com but although it says it is not claimed, it uses a redirect and is.
Instead I snagged myself a Dave Naylor page
The reason it’s important to be the first is that if a load of people also give it the thumbs up, your Stumbleupon account becomes more powerful.
So grab it whilst you can.
It’s not supposed to be on by default (and it wasn’t for me). It’s in Toolbar >> Configuration >> Highlight recommended search options.
That feature has been around since september: http://googlesystem.blogspot.com/2006/09/stumbleupon-integrates-with-search.html
Interesting that a stumbleupon upgrade puts it into default.