First it checks if you have installed the latest version. If you have it does nothing. If you doesn't have the latest version it will replace the java file inside KoLmafia.app in your applications folder.
I made this script in applescript and here are the requirements:
*Have KoLmafia.app located in Applications folder (Can be downloaded here: https://sourceforge.net/projects/kolmafia/files/ remember to rename "KoLmafia.14.0.app" to "Kolmafia.app")
*Added option to run KoLmafia after trying to update.
Update 26. Feb 2012:
*Supports lion now
*Don't download temporary version file to downloads folder
Update 26. Feb 2012 (again):
*Allow KoLmafia.app to be in any location
*Ask for confirmation and quits KoLmafia if running before updating.