http://thekage.stumbleupon.com/ I found it kinda funny, considering some of my sites only have a PR of 2-3.
Only problem it does not help sites pr because they use no follow tags. I guess if you have some good links it will help traffic but not Page rank of those sites.
My stumble upon page has a page rank of 5 now according to the new update (didn't have any pr at all before the update though). Not sure if its going to stay at pr5 either...
Pagerank on social media pages is a joke. my stumble page has 104 BL and P3. My site has 3000 BL and still PR3. Google is having a brainfart.