The magic of Chatroulette wasn't the very real possibility that you'd meet a penis or seven being stroked or otherwise touched in the creepiest way possible, but by the sense of total serendipity. Anything or anyone could be on the other side of the click.
While there's always certain feeling of that when you click on links, whether they're from Twitter or Tumblr or wherever — where am I going? — there's always a sense of direction. An idea of where you're going. XKCD's Holistic Browser throws that sense of direction out the window, replacing it with that kind of pure serendipity. When you punch in a URL, it takes you to a website randomly chosen by somebody else. You really have no idea where you're going to windup: A keygen site, a comic, or yes, maybe you'll be looking at some dicks. But that's precisely the magic of it.