You can reclaim around 200MB of hard disk space following an install of SP2 (Need to have disk formated in NTFS though).
Find the following folder in your Windows directory:
Right-click and select Properties > Advanced
Select the 'Compress contents to save disk space' check box
Click OK, and when you see the 'Confirm Attribute Changes, select the 'Apply changes to this folder, subfolders and files' radio button
It will take a few minutes for the compression to take place.