Social bookmarking sites revenue?

Question From User - Answers in Comments.

What do you think how much would be the revenue of social bookmarking sites like reddit, stumbleupon, digg, etc (minimum to maximum)
I MEAN BY REVENUE OF THEIR SITES AND NOT THE SITES WHICH ARE UPLOADED ON THEIR SITES
I MEAN BY REVENUE OF THEIR SITES AND NOT THE SITES WHICH ARE UPLOADED ON THEIR SITES