Apparently the guys from Mojang forgot to do an svn clean before packing Minecraft.app (the MacOS package):

costo:Minecraft.app acoster$ svn status
M       Contents/Resources/Java/MinecraftLauncher.jar

costo:Minecraft.app acoster$ svn info
Path: .
URL: svn+ssh://notch@mojang/home/svn/repo/minecraft/trunk/Launcher/Minecraft_Mac/Minecraft.app
Repository Root: svn+ssh://notch@mojang/home/svn/repo
Repository UUID: 7aa861d8-b6c6-428c-ac33-4288b91362a4
Revision: 154
Node Kind: directory
Schedule: normal
Last Changed Author: notch
Last Changed Rev: 154
Last Changed Date: 2011-02-23 11:51:17 +0100 (Wed, 23 Feb 2011)

You can even revert to a previous version (although I didn’t bother trying to run).