Reclaim HDD space on Windows 7

Collection of tips on getting some more free hard disk space. Applicable to Windows 7.
WARNING! use carefully, not all tips are applicable to your situation

- Use Disk Cleanup and free space occupied by SP1 backup files, if you never going to rollback to pre-SP1 state
- (Useful for desktop PC, may be harmful for a laptop) This will disable the hybernation feature, in theory should free up the same amount of HDD space as you have RAM. Run as administrator in command prompt:
powercfg -h off

Some tips on reclaiming the disk space on windows

Watch this space. Some tips on how to free up some space on your hard drive if you had fairly recent Windows OS installed (Vista, Windows 7, Windows Server 2008, etc)

%WINDIR%\SoftwareDistribution\Download - delete whatever is older than 10 days there. Later files may still be needed by ongoing Windows Update

%WINDIR%\Installer\$PatchCache$ - mostly safe to delete.

DO NOT however delete whatever is in the root of %WINDIR%\Installer !!

download msizap utility which comes in Windows Installer SDK - http://msdn.microsoft.com/en-us/library/windows/desktop/aa370834(v=vs.85).aspx - and run it with g option, i.e. msizap g - it will delete orphaned windows installer files. Other options of this utility may be risky - general rule is that messing with windows installer files that are in your windows folder may break your system and you will need to reinstall it.
More info on msizap: http://msdn.microsoft.com/en-us/library/windows/desktop/aa370523(v=vs.85).aspx