I remembered something the other day. The new multiplayer maps in Minecraft 1.8 show the map's seed when you press F3, people can use this to their advantage to generate that map themselves and cartograph it to find diamonds, dungeons mineshafts etc. There might (or might not) be a 1.8 bukkit server plugin to removes it, but if there isn't it might be a little problem. If we could trust everyone who joins I assume I would be fine but just in case.
Just thought I'd tell you that in case you didn't already realise