I covered this morning the news that eBay is launching a contextual advertising program named eBay AdContext. The program uses contextual based technology to match eBay auctions with the content from the publisher's Web pages. Publishers will not get paid on a PPC or CPM basis, but rather it seems like they will be paid a commission of the sale generated from the click. The commission percentage seems to be as low as 35%, according to CNN Money and as high as 70%, according to USA Today.
I suspect those who run Google AdSense and/or Yahoo Publisher Network would not be allowed to run eBay AdContext. But the two programs, eBays versus Google's and Yahoo's are pretty different, in that one is promoting auctions and the others are promoting a pool of advertisers bidding on keywords.