Any country that attempts to do that has to be kidding. Bitcoin is anonymous for christs sake so how would you plan on blocking it when you dont even know who is carrying out the transactions.
It's actually not that hard.The chinese firewall for example might do the trick with some tricks added.
Right now bitcoin uses for default port 8333 and the number of users actually capable of forwarding a port might be less than 0.1 % of this board.
But if they were totally against bitcoin and try to make an example of it they could do it far easier.
Declare it illegal and then have 50 or 100 people executed in a stadium like they did a month ago with 13 drug dealers.
Are you going to risk your life for bitcoins? Doubt it.
