[JonnieCache]

As someone who was a university student recently, I can tell you that the standard stumbleupon usage pattern goes like this:

    1) Click stumble button
    2) Look at page for 0.5-2 seconds
    3) Stay on page if it's the kind of thing you're looking for (usually novel flash
       games or funny videos,) otherwise go back to 1.

The mouse pointer typically never leaves the stumble button during this process, we used to flick through dozens and dozens of pages like we were doing a psychoanalytic free association excercise until we found something we liked.

So yeah, not exactly high quality traffic.