I absolutely love the Add/Remove Programs tool within CCleaner, it's an assload of times more organized and easy to use than the one built into Windows, especially with the Delete Entry option which keeps me from digging through the registry manually (which I can probably safe say we all hate to do).
However, the only reason I keep going back to Windows' Add/Remove Programs is because of the fact that it shows the estimated amount of disk space the installed item uses. This feature would be a welcome feature in CCleaner.
Along with this, Add/Remove Windows Components is another feature in Windows which I come back to every so often. While this wouldn't be a priority to have in CCleaner, It would be a nice addition as well.