Hi,
I've tried CCleaner in my officer to clean off some cookie information. I have installed Flash player debug version along with Flex Builder 3 for RIA development. CCleaner deleted some files in C:\Documents and Settings\[username]\Application Data\Macromedia\Flash Player\#SYS\ folder and the application crashed unable to load the application system settings from that folder stating some "Security Sandbox Violation" in Flex Builder 3. Once I uninstalled Flex Builder 3 and installed it again it worked fine.
So it would be fine if it doesn't delete those files in the future version.
Thanks,
Karthik R