It's common knowledge that sensitive data such as passwords etc are stored unencrypted in the Windows swap file, and that the swap file is not cleared by Windows.
I think it would be usefulto have CCleaner be able to overwrite the Swap File with zeroes.
Windows can be set to zero the swap file (once when rebooting) using the registry entry (swiped from http://www.iusmentis.com/security/filewiping/wipeswap/):
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\Session Manager\Memory Management\ClearPageFileAtShutdown
REG_DWORD
Range: 0 or 1
Default: 0
(When the entry is set to 1; Windows will fill the paging file with zeroes when exiting.)
CCleaner could set this entry. Or, even better, you could have it encrypt the swap file using a resident driver.
james