It would be very neat if the program were to be country-aware. I’m still looking for a way to block/allow whole countries (you know who you are) for certain applications like my mail server. Since the country database is licensed by MaxMind, Comodo could use the free GeoCountry Lite database as a plugin, like for example dc++ does.
To be able to import a list from a file in a zone would already do a great deal, the format needs to be defined though, but doesn’t have to be complex…
I’d like it if you could use wildcards in hostnames when defining a blocked zone. E.G. Entering “*nz” as a host name would block all domains ending in “nz”. While this wouldn’t catch all domains in new Zealand, it would catch a large percentage of them.
Cheers,
Ewen 
That only works if reverse DNS is properly configured, which in case of Spammers it often isn’t. Plus, the DNS resolving introduces another overhead. Don’t get me wrong, I’m all for it as well if it feasible but I think a lookup in an external IP database would be much faster.
I like this idea. I had a spam filter that I could block by country and it was incredibly useful. It also showed graphs of the filters in use so you could see just how much was coming from the blocked countries. A real eye opener!