It would be really useful to be able to create placements that only show to people in specific geographical locations, with "include" and "exclude" selections for countries.
For example, if my site has a mix of both UK visitors and visitors from other countries, I'd like to be able to create two placements for the same zone that are set up as follows:
Placement 1 - For ads targetted at UK visitors - Set to "Include" United Kingdom
Placement 2 - For ads targetted at Rest of World - Set to "Exclude" United Kingdom
That way, my UK visitors will always be seeing the most relevant ads.