I've been reading this thread with interest because there is a offer out there that allows advertisers to pick specific placement on publisher sites. The service is called Pagematch and it's offered by Quigo's AdSonar.
I'm a travel agent who does a lot of my own work on the web and I found that contextually relevant advertising just wasn't showing me the kind of ROI I was looking for. I was about to cancel my account with AdSonar and one of their reps told me about Pagematch. I could bid for specific placement on several sites.

I advertise on the USAToday.com home page, the DenverPost.com homepage, DiscoveryTravel home page and a few of the smaller travel sites. The bids start at about a dollar or two, depending on the page. It's been great for me - it's a far more cost-effective way for me to advertise my business than through contextual. From what I've heard they offer this for about 40 different high-traffic pages.

AO

There are engines like BlowSearch that have this ability to block publishers. I do not see Google committing themselves to this anytime soon. But eventually it may be the easier way of them countering fraud or at least stop the advertisers who are savy enough to find it from constantly bitching about the handful of bad sites.

Looks like recent events may indicate Google paid some attention to AdSonar in designing their latest iteration of content targeting?

I think there has definitely been the feedback to Adwords from people who wanted to target specific content pages/sites. Who wouldn't want to have their ads appear on their competitors sites who also happen to be running AdSense ;)

I am pretty pleased they are finally allowing it. I am also curious to see what Yahoo will pull out of the hat to compete as well.

It is also unfortunate that AdSonar has not expanded to more market areas beyond the handful they currently do. It is really limiting their position to become a contender for publisher's page space in the contextual ad market.