So, 1.2’s a little slower for some reason and I wanted some speed. I did a little googling around and found a few ways to enable x86_64 capabilities with the OSX Minecraft client.
Minecraft’s JavaApplicationStub needs to be replaced, so back it up then link the new one in by running the following commands from [Terminal](http://en.wikipedia.org/wiki/Terminal_(Mac_OS_X):
cp /Applications/Minecraft.app/Contents/MacOS/JavaApplicationStub /Applications/Minecraft.app/Contents/MacOS/JavaApplicationStub.orig
ln -s /System/Library/Frameworks/JavaVM.framework/Versions/Current/Resources/MacOS/JavaApplicationStub /Applications/Minecraft.app/Contents/MacOS/`
Add 64-bit to the application’s capabilities by running the following command:
/usr/libexec/PlistBuddy -c "Add :Java:JVMArchs:0 string 'x86_64'" /Applications/Minecraft.app/Contents/Info.plist