I don't typically play MP, but I've seen a number of comments go around regarding better Anti-Griefing tools or just limit player access to your worlds...
It's hard enough, IMO, to find and hook up with people that you are willing to play with... and even they, you really don't know much about how they will play until you get them in your world and see what they do...and even then, there is a huge blind spot about what they are or are not doing when they are not within range of you... and you are expected to monitor their activity on top of it instead of play the game yourself? Or you can gimp the players so they can't do anything at all that is worthwhile and makes playing MC more fun.
If you want players to have full access to all the normal play features of the game, then you really don't have an effective way to limit griefing before it actually happens other than trusting the players. However, the tools to handle griefing after the fact are limited in the Host's ability to detect Griefers and restore the game state to a previously saved state.
I was looking at how Wiki Pages were designed, and thought this would be a marvelous tool for a host, the down side is that it would require a bit more HD space than simply a single saved game file, and might require some RAM dedicated to tracking and collecting Log File information.
But basically, a Log File could be created to periodically track player position in the world (X,Y,Z,plane), log block changes, item changes, (chest) inventory changes, etc. as well as track Player induced changes with time stamps.
And Like a Wiki, could use the Change log to restore the world to any specific previous Log File point, or just keep tabs on multiple saved game files instead of just one.
This would help the Host be able to go through their logs to determine which player is causing Griefing problems for him and his players, and work on banning them from the game in the future and undoing some of the damage that was caused by their destructive participation.
I'd also implement a 'Blacklist' of Players that would not be able to participate at all on that Host's 'Open' games/maps, let alone the closed games/maps.