I found the answer on the minecraft forums, so I'll repost it here.
http://www.minecraftforum.net/topic/36564-minecraft-on-osx-wont-open/
Thanks to
ahefner said: The bundle doesn't work because some unix file
permissions get screwed up as a result of distributing the app bundle
inside a zip file (versus, say, a .dmg). You can fix it from the
terminal using the chmod command as follows:
chmod +x ~/Downloads/Minecraft.app/Contents/MacOS/JavaApplicationStub
Modify the above command to reflect where you unzipped Minecraft at.
This will fix the bundle so that it opens when you click it.
Minecraft on Mac OS X with 64-bit Java
So you're a slave to warning messages and you want Minecraft to use 64-bit Java. Here's how to do it on the command line. These instructions were crafted on MacOS Lion, which should prefer 64-bit Java when possible (Applications/Utilities/Java Preferences). These instructions assume the default Minecraft.app location, in the main /Applications folder. I had a few tabs open, while I was sussing this out, including an excellent forum post, a post on JavaApplicationStub bits, and the official reference for CF keys.
Here we go.
Swap out Minecraft's JavaApplicationStub for the current OS' version:
gzip /Applications/Minecraft.app/Contents/MacOS/JavaApplicationStub # save a backup
cp /System/Library/Frameworks/JavaVM.framework/Versions/Current/Resources/MacOS/JavaApplicationStub /Applications/Minecraft.app/Contents/MacOS/
Then, add 64-bit architecture to Minecraft's possibilities:
/usr/libexec/PlistBuddy -c "Add :Java:JVMArchs:0 string 'x86_64'" /Applications/Minecraft.app/Contents/Info.plist
Launch. That should do it. Watch out for creepers. Have a nice day.
If everything goes wrong, here's how to roll back from here to your original configuration:
rm /Applications/Minecraft.app/Contents/MacOS/JavaApplicationStub
gunzip /Applications/Minecraft.app/Contents/MacOS/JavaApplicationStub.gz
/usr/libexec/PlistBuddy -c "Delete :Java:JVMArchs:0" /Applications/Minecraft.app/Contents/Info.plist
I did not write this! Source
Best Answer
Try adding my ram to the launcher. Click
optionsat the top and drag the ram slider:I believe unleashed requires at least 2.5GB ram to work properly and recommends at least 3. Don't drag it above 4, as it will mess with Java.
Also make sure you have 64-bit java on a Windows computer (this does not matter on OSX).
I also suggest switching to the Direwolf20 (DW20) 1.6.4 pack as it uses a newer version of Minecraft, has updated mods and is slightly moer optimized.