Just to remind you, that like every cluster of society, there's just a few bad apples... I don't understand why do you want to do that
I plan on doing the exact same thing with my site as soon as my hosting company can add GeoIP to the server.
The vast majority of hacking and spamming attempts on my site originate from IP addresses in China, Russia, Korea, Russia, Germany, and a few others. Due to the nature of my site, there is simply no reason to allow IP addresses from those countries access to my site since the likelyhood of a single legitimate user from those countries is near zero.
While in many cases blocking entire countries is illogical, in my particular case it makes perfect sense.