Apparently no one clicks on display ads on social networks anyway. That probably explains the sharp dropoff after MS and FB. And FB is aiming high since their lowest meaningful entry-level ad package costs $50K.
It’s just that social networks number 3 and beyond get about 2% of the total traffic of FB+MS combined. And display ads are bought against volume, not relevance. Plus I bet the CTR on blackplanet.com is way higher than FB.
So do we or don't we place ads on these things?