Delete designable.nib and Gain Space From Your OSX Leopard Installation
Deleting the deprecated "designable.nib"; files from your apps should regain a bunch of space:
find /Applications/ -depth -name 'designable.nib' -exec rm '{}' \; -print
Could break everything though :) Don't say I didn't warn you.
And for people who really want an explenation and the raw numbers: click here