I have Comodo Syscleaner (4.11.2010) installed on Vista 64-bit with all updates etc.
For a long time I have had problems removing USB stick using the built-in facilities. They always complained that the drive was in use, even if I had closed all windows & apps etc.
To be sure nothing would go wrong, I had to shut the system down just to remove a USB stick :-(
I finally started looking around for a solution. A trial install of one of the USB removal utilities - Safely Remove USB - tells me that it thinks Comodo Cleaner Cleaner_validator.exe is using the drive - which explains why Vista won't let me remove the stick.
With this information, I opened up Syscleaner and disabled Active Clean and I can now remove my USB Stick safely.
I wish I had known about this 'feature' and its implications - because it really has left me with a bit of a bad taste ....