Well, it looks like StumbleUpon can actually be used as a kind of a search engine. It's apparently a beta feature. When you click on the interests button, in addition to all the interest categories there is now an "Explore an interest" field where you can enter anything you want. I got pretty good results with some more general queries. It certainly wont be very useful if you're looking for a specific model of something or anything detailed like that, but if you're looking for something more general like "sleep disorders" or "digital DJ", something it could treat as a category or a tag, the results can be very good.
Of course, results aren't displayed like in Google. You simply get the first page displayed, perhaps randomly, and keep stumbling until you get to a satisfactory page. I think the best thing about this is already mentioned ability of SU to bring out really good pages that might be buried in Google.
It's work as a food for my hungry mind... I'm newbie so these stuff actually helping me alot :)
Originally Posted by bogart
Actually, it still lack of more users as FB. and FB is very strong competitor of it in case of social networking features.
I haven't used Google + from the last 4 months. This can tell you about my views on Google +.
On the other hand, websites like Stumble, Digg, Traffup, Twitter, Facebook, Hubpages, Squidoo, Delicious, Reddit provide amazing traffic on my blog.