Sincere request: Can somebody explain the dynamics of how Stumbleupon is so popular? I don't know anybody who uses it. I am friends with alpha-geeks, teenagers, senior citizens, native Spanish-speakers in Mexico, etc. Barely anybody I know uses it. I had a StumbleUpon account before Twitter, before StumbleUpon was a URL shortener, etc. I used it a little, but people didn't seem thaaaat into it. There must be some poc…
I think it's less popular than these stats might indicate. 1 Facebook user might click on 1 or 2 links per day. 1 SU user "stumbles" dozens or hundreds of times in a session. A stumble nets a pageview, but obviously has considerably less value (no intent baked into the click).
It's like a youtube party, but with a little fast-forward button: http://xkcd.com/920/