Leaderboard

http://minecraft.gamepedia.com/Minecraft_launcher#Command_Line_usage

Create a new instance of your IWorldEventListener for each World and store the World in a field. ServerWorldEventHandler and RenderGlobal both do this.

Which clients need which data and when? If a client always needs to know a particular value (e.g to render it on a HUD), send a packet to any relevant players when they log in and when the value changes. If a client only needs to know the value in a GUI, you can probably sync it through the Container (either using the built-in syncing packets or your own). If a bank account is only ever linked to one player, consider storing a player's bank account(s) in a player Capability instead of using World Saved Data.

I make the blocks actually fall - I made a custom falling block entity that moves sideways as it falls, so that the blocks end up going roughly diagonally like a real tree. Here is my entity class - I've got slightly different behaviour for logs and leaves, to make sure that logs are prioritised as much as possible and fall through leaves that are in the way.