When Snow Leopard first game out, it was promised to cut back on the OS footprint (in Gigs).
Now, upgrading to 10.6.5, I somehow had insight to take screenshot of disk usage right before upgrading and comparing to the after shot:
As you can see – it freed over 2 GB of disk space. Now this is what I call a good upgrade. Not only adding features and fixing bugs, but at the same time cutting back in bloat.
Note: my Time Machine reported 7.03 GB worth of changed data that needs to be backed up. So get some, loose some. But as my backup drive has lots of space while MacBook has little, I consider myself a winner.