Rated 2 out of 5 stars
I liked stumble upon. A good idea. But StumbleUpon is near dead whether you know it or not. Many users warned them about it, but I guess quantity wins against quality once again (although they could win both).
@proxim2020 is right, stumble upon isn't what it was a year ago. Google have been making the same mistakes recently, giving less customization options and orienting users in a certain way by using the illusion of "graphical pleasantness" and "choice". Man, it looks like 2000s vs 2010s will be worse than 70s vs 80s (80s vs more-crappy-80s, maybe?).
I'm leaving SU, too, until they get it together. But SU has a big potential, it was great once. It can achieve this again, by not-regarding its users as products.