Some clever Spanish chap has posted up on PSX Scene a very useful program for trimming down the size of your PS3 backups. Apparently one chap got GOW3 from 45 gig down to about 22 gig using this program. It basically gets rid of all the files not needed like updates/languages/dummy files etc.
Here is the link :
On page 2 of the thread there is a version 2.0 that has been released. The only downside is that the program is in Spanish but it looks pretty straightforward to use
ABSOLUTELY NO LINKS TO FILES ON DF PLEASE ! (4me2)