I like John Blackbelt Jones ideas about blocking hosts except for some subnets / backbones domains or IP.

Would be greate for eg university networks with speeds like 2,5 Gbit/s and 10 Gbit/s (sunet/nordunet), or for better crawling in northern Europe, and to get rid of all american modem users and theirs futile attempts to download iso-files.

/Mutatis mutandis