In response to the discussion on Video Demonstrates PPC to PPC to PPC Pages Via Google AdWords & AdSense Network at WebmasterWorld the AdWords representatives noted that you can exclude your ad from coming up on the content networks and park domains. In reality, you can exclude your ads from showing on the content network, which I believe is the parent of the parked domain service.
For example, in the "Edit Campaign Settings" section of your campaigns, you can define which Google networks you want your ads to run on. Here is a picture of that.
You can have your ads run on Google.com only. You can have your ads run on Google's search network (explained here). And you can have your ads run on the content network (explained here). Which network does the park domain program fall under? It is not 100% clear to me from this documentation, but I believe it would be the content network.
Does this solve all of the advertisers issues? I doubt it.
Forum discussion at WebmasterWorld.