There have been publishers in both the Google AdSense network and Yahoo! Publisher Network who were banned due to their ads running on sites that were not appropriate. Some publishers are worried that it may happen to them.
A WebmasterWorld thread asks for Google to add an allow domain feature.
This feature will allow the publisher to specify which domains or IPs can show this publisher's ads. If the domain or IP is not allowed, the ads will not show. A security blanket for some worried publishers.
I like the idea.
Forum discussion at WebmasterWorld.