In the past month I used a few different ppc networks to run my holiday promotions. These are the networks I used:

Facebook

Google AdWords

7 Search

Bidvertiser

Yahoo

MSN

From the list above the overall winner would without any doubt be Google AdWords. The most traffic was generated through AdWords and some programs had a very good convert rate which turned into sales. The next best network I found to be 7 Search. I ran a few programs only on this network and did get traffic and conversion. The slowest to get traffic and had no conversion was Bidvertiser, in order to be fair with Bidvertsier perhaps I did not set the campaign correctly. As for Yahoo and MSN I did get a little traffic nothing major and little conversion. As for Facebook some campaigns worked well other did not, I did like Facebook. The only thing I do not like about Facebook is the Facebook Police that rejects almost every ad submitted. It took me a good 10 submits of one ad before the Facebook police let me run the ad. If you are going to spend money and want to see results Google is the way to go. The other networks are great if you can set cheap bids and just let them sit there to run when your bid is the highest.