Enable the Minecraft Launcher in OS X Yosemite

MinecraftEnableYosemite.command

echo "This assumes you have Minecraft installed at /Applications/Minecraft.app"

cat << 'EOF' > /Applications/Minecraft.app/Contents/MacOS/Minecraft
#!/bin/sh

PRG=$0

while [ -h "$PRG" ]; do
    ls=`ls -ld "$PRG"`
    link=`expr "$ls" : '^.*-> \(.*\)$' 2>/dev/null`
    if expr "$link" : '^/' 2> /dev/null >/dev/null; then
        PRG="$link"
    else
        PRG="`dirname "$PRG"`/$link"
    fi
done

progdir=`dirname "$PRG"`

if [ -n "$JAVA_HOME" ]; then
  JAVACMD="$JAVA_HOME/bin/java"
elif [ -x /usr/libexec/java_home ]; then
  JAVACMD="`/usr/libexec/java_home`/bin/java"
else
  JAVACMD="/Library/Internet Plug-Ins/JavaAppletPlugin.plugin/Contents/Home/bin/java"
fi

cd "$progdir/../Resources/Java"

exec "$JAVACMD" -classpath "$progdir/../Resources/Java/*" \
       -Dapple.laf.useScreenMenuBar=true \
           net.minecraft.bootstrap.Bootstrap

EOF

chmod a+x /Applications/Minecraft.app/Contents/MacOS/Minecraft

rm /Applications/Minecraft.app/Contents/MacOS/JavaApplicationStub

xattr -d -r com.apple.quarantine /Applications/Minecraft.app/

defaults delete /Applications/Minecraft.app/Contents/Info.plist Java
defaults write /Applications/Minecraft.app/Contents/Info.plist CFBundleExecutable Minecraft

echo "Minecraft has been patched"

So, the deal is, you download MinecraftEnableYosemite.command, double click it and - as long as you've got a FRESH copy of Minecraft at /Applications/Minecraft.app (as in, you've just downloaded it and never tried to run it), and a working copy of Java or the JDK (I suggest the 1.7 JDK) - it will patch that application to work properly in Yosemite.