Sadly, I am sure griefers are problems on just about any public server. :| People just have nothing better to do...
I think all griefers are basically 3 groups.
1. Jealous types who grief good builds because they can't build that.
2. Team aVo fanboys who want to follow in their footsteps by placing blocks everywhere or trying to destroy stuff.
3. The type who grief and leave the server, basically they block a couple houses.