You know how in Super Mario World there are the blocks you can hit to bring up a message? They used them for hints and stuff, "Jumping on koopa shells will keep you out of the lava," etc etc etc. How about a block that only OPs can use, basically you'd use it like this:
/info Thanks for joining my Minecraft server! Please be courteous to those around you and behave, you will be asked to return!
Then when you hit enter a block appears where you were targeting, when a player hovers over the block either a message window appears after a few seconds or a notice comes up "Read - Z", and then you could press Z to bring the window up, which would read.. "Thanks for joining my Minecraft server! Please be courteous to those around you and behave, you will be asked to return!"
You could even have a second version of the block that users could edit (but not place). There's so many practical uses for this, such as a rules board, notices, admins lists and contact info, site information, uptimes/downtime notices. And for the second version, well, clearly it'd be some kind of community bulletin board.
This feature could increase communication flow, add a whole new level of detail into the game, inspire creativity, and above all else its not all -that- complex of a feature to conceive for programming. I can promise that it would be an update EVERY administrator would thank you for, and if you added a community-edit version on the side, everyone could reap the benefits.
I think this would be extremely useful for rules alone, and it would convince me to use honeycomb prisons rather than single cells, too. Directing people to rules that exist outside of the game (and often outside of the minecraft forum) is very cumbersome and inconvenient. It would also be nice to have an OP rules block that I could keep updated on what is and isn't expected of operators on my server, what is bannable or warnable, etcetera.