A replica of Denmark in Minecraft, which was reported here, has been vandalised with some areas blown up and flags of the United States created.
Only a small area was destroyed and the flags appeared near the starting point, which points to just attention seeking as opposed to a virtual liberation attempt. Other players have cleaned up the damage, replacing it with green grass and flowers.
Wow, hosting a service that anyone can go on and write what they like, how stupid could they be! *scoff*
Ohhhhh wait... ;)
Vanilla Minecraft is pretty light on CPU and RAM, but the unithreaded world update routine doesn't help at all. The real implementation problem is bandwidth, although 3D-defined chunks instead of 2D ones would have made a big difference there.