I've been experimenting with paid traffic sources (figured paid traffic is black-hat, move the thread if you disagree), most recently I chucked some cash into StumbleUpon Paid Discovery. If you've not seen this before, essentially you are paying to be shown to StumbleUpon users - rather than leaving it to their random-chance/organic stumbles. The user see's that your page is a paid/sponsored stumble in their menu-bar at the top. I set-up a Blog post, properly written ~500 word article with a dozen or so pictures linking off to other pages on my site. Professional looking Wordpress theme squarely aimed at the Female demographic, Adsense Wide Skyscraper in the sidebar runs parallel to the article. I setup the campaign to target only Female users with one matching Interest relevant to my niche. My $17 apparently bought me 170 paid stumbles, server access_logs showed only 154 visitors with stumbleupon as the referrer and Google Analytics reports just 39 unique pageviews with a bounce rate of 18.42% (pretty low) and an average time on site of 10 minutes 23 seconds. In conclusion, the bounce rate and time on site is quite extraordinary compared to other paid traffic sources I've seen lately. The sample size of 170 visitors was quite small, I didn't get any Adsense clicks etc. I might reinvest more later into a larger experiment, from what I can see there is no difference between the paid and organic referrer URL so I'm not sure how Google Adsense will look at this.