Developers are starting to distribute binaries that will run on Intel-based hardware as well as PowerPC Macs. This will add about 30% to the size of the executables. To recover the disk space, you can remove the unneeded code using the command-line program ditto.
For example, suppose Foo.app is a fat application bundle installed on a PowerPC Mac. While logged in as an admin user, you would open a Terminal window and type something like:
ditto --rsrc --arch ppc /Applications/Foo.app /Application/Foo-ppc.app
Now you have a new application called Foo-ppc.app. Test it. If it works, you can delete the original and rename the stripped version. To strip PPC code from binaries on an Intel Mac, you would change --arch ppc to --arch i386 in the above command.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050810112422666