buckworks - 10:41 pm on Apr 11, 2012 (gmt 0)
it's easier to advertise on hundreds (or thousands) of websites without having to identify them ...
However, keep an eye on your performance reports because you'll sometimes spot sites that are clearly a better fit for your ads than average. Look for things like better conversion rates, lower cost per conversion, lots of view-through conversions, etc. Those gems can be good candidates for direct contact, or at the very least, bidding more aggressively for placement via AdWords.