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.

Comments:
DazzlinDonna
04/30/2007 01:18 pm
Actually, publishers have been asking Google for that feature for quite some time. But as is typical, it will probably take an A-lister to make an issue of it before they will take notice.
Barry Schwartz
04/30/2007 01:20 pm
I bet... Just have not seen it in threads.
David Saunders
04/30/2007 01:35 pm
I think it should and will happen :)
Lea de Groot
04/30/2007 02:07 pm
And if, for some strange and unlikely technical reason, they are unable to do that then, an auto 'show me the domains my ads have appeared on' option in the reports would be a good second best, as an alternative to listing the domains you'd like reported. (I see a checkbox at the top of the 'channel selector') This would let Sally Publisher shoot off a fast email of 'thats not *my* domain those ads are appearing on!!' when needed. Not as good, but better than the current nothing. :(
Nightmare Before Christmas
05/24/2007 11:22 am
I've been asking them for a while now, but nothing yet !