But what sort of traffic?

See, e.g., Arvind's comments on StumbleUpon visitors:

http://arvindn.livejournal.com/133249.html

To quote the takeaway, "most of the traffic generated by StumbleUpon users to any given site is going to be low quality because the dopamine junkies make 100x more clicks".

As far as I can tell, SU traffic is almost useless. I may get 1,000x as hits from SU, but I derive more value from some hole-in-the-wall site writing about me and sending 20 people.

Very true. StumbleUpon shows a much higher bounce rate and much lower average time on our site.

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 pocket of main use-case there. Is it mostly the URL shortener that even non-S.U. users bounce around in when directed to a su.pr URL?

I'd love to understand this.

(Also, as somebody else pointed out, S.U. traffic is pretty low-quality. Just peep your Google Analytics, and those sessions are quite short compared to Twitter/FB/Tumblr referrers. At least on my sites.)

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).

Quote from a friend who stumbles: "oh yeah. totally. i hit 100 pages and maybe read 5 of them"

It's like a youtube party, but with a little fast-forward button: http://xkcd.com/920/

I used to use it heavily, but I stopped when I moved to Chrome, since at the time it didn't have Chrome support and even now it feels hacky.

Worth noting that SU traffic may be unusually low-engagement, since I would think it's likely a user will just click Stumble again after the half a second or so you get to grab their attention. (That's an educated guess, mind you--I don't have any data to support this beyond how using SU felt to me.)

I was wondering the same thing. I've never had the inclination to even go to their website.

Among my friends (university students, canada), it's pretty much used for idling wasting time when we need to give reddit or youtube a break.

My site ThatHigh.com consistently gets a ton of traffic from SU, in disproportionate amounts. I'm fascinated by how massively successful that service is. The traffic has been steady for over a YEAR now. And it shows no signs of stopping.

And yet I know so little about it. I know they have something like 10M active users, which seems really high.

My facebook traffic is starting to pick up, but it's still no where near StumbleUpon.

Compare: http://i.imgur.com/oY03q.png

It's been like this since 2008.

What is the quality of the visits like? When you factor in time on site, pages viewed, bounce rate, etc. is stumbleupon still providing better traffic? It might be, but the answer isn't obvious to me without knowing this type of data.

Depends what you're looking for. If you're being paid by CPM, then yeah, they're great visits. If you're looking for conversions, then probably not.