If you open Control Panel, Performance Information and Tools, Advanced Tools, and select "Generate a system health report", Windows Vista will, after approximately one minute, generate a system diagnostic report showing potential areas that could be affecting your systems performance and reliability.
The information for these reports is created in "%systemdrive%\PerfLogs\System\Diagnostic\<date>" and can be viewed immediately upon creating the report or at any other time from the Reliability and Performance Monitor (Reliability and Performance, Reports, System, System Diagnostics, <date>).
The reports can be deleted manually from the Reliability and Performance Monitor, but it would be nice to have the option included as standard in CCleaner. If the PerfLogs folder or its subfolders are deleted, they are automatically recreated by Windows as and when required. Also, the folders appear to delete successfully even with User Account Control turned on (which I prefer).
Regards
DJ