In the past I have not been discouraged from using a portable 32 bit CCleaner on a Flash drive on a 64 bit machine.
I now believe this is dangerous.
I have learnt that x64 bit Windows tells lies to 32 bit applications,
and when the application attempts to deal with system32, the Operating system is secretly aiming it at SysWOW64
http://forum.piriform.com/index.php?showtopic=32083
I find that WinApp2.ini includes many targets within system32,
so the reality is that the 64 bit DLL's which live in System32 will not be zapped,
but only the 32 bit DLL's in SysWOW64.
WinApp2.ini also has at least one DetectFile which uses System32.
I know nothing of the inner workings of CCleaner.exe itself.
It seems to me that x64 bit CCLeaner on a x64 bit machine will do a good job for x64 bit applications,
and will correctly target their x64 bit DLL's held in System32,
but it will NOT deal with SysWOW64 and its 32 bit DLL's unless specifically coded.
I believe that x32 bit CCleaner will be diverted to 32 bit DLL's in SysWOW64, and the x64 bit O.S. will not let it anywhere near the 64 bit DLL's in System32.
I do not know what disasters may lie ahead,
I just do not like wiring up to a mains power socket where the Live and Earth have been swapped over,
it is against regulations and it can kill people.
I have not worked out the specific mechanism of a disaster due to Windows deception,
but I have a bad feeling about it.