This may not be a new occurrence, but for the first time my eyes have seen third party advertising within StumbleUpon in the form of Google AdSense.

StumbleUpon uses the pay per stumble advertising model for companies which wish to draw more eyes to their web properties. However, it now seems that StumbleUpon, a bookmarking and web navigational social network, is now testing alternative forms of revenue generation via serving Google AdSense ads (pub ID : pub-4790703644985743).

One question which comes to mind is that if StumbleUpon is an eBay company, why is it serving Google’s contextual advertising?

eBay has a very important partnership deal with Yahoo where Yahoo uses Paypal as its payment system of choice while eBay is serving Yahoo Search Marketing and Yahoo Display Ads on eBay properties. One would think that Ads by Google on StumbleUpon would show a bit of conflict in the eBay & Yahoo agreement.

StumbleUpon may still be running as its own autonomous company however, which would explain their use of Google AdSense.