When I recently upgraded from Tiger to Leopard I didn't notice much of a change in disk space. Saying that, I did also have a change from a G4 to a MacPro....so I might have just ignored things. If you are worried about your hard drive space and the room your OS takes up you can save a lot of space by getting rid of languages on your hard drive. Anywhere from one to as much as 3 gigs of space can be "saved by cleaning out the languages you will never use. You can do that with a free app called.... Monolingual. It not only removes the languages from your OS, but also languages in your apps. I removed all but a couple of languages and saved 1.8 gigs..... it just depends on how many and what your apps are.