Where has all my (Windows) space gone?

Windows 7 & Windows 2008 need 20Gb or so boot volume to start with and 50Gb or more is recommended. But even with this the free space will vanish rather quickly.

Some of this is due to stuff in the installer directory and the side by side (SXS) directory - and NO! - don't delete stuff from here! - but it's also worth looking in the Windows Error Reporting directory - C:\ProgramData\Microsoft\Windows\WER\ReportQueue

These error logs should be automatically uploaded to Redmond and then deleted but often are not. This seems especially true for Exchage boxes where 2 Gb or more error dumps are common.

And yes, you can delete these with no problems!