It would be nice to be able to save a "selections state" as a preset that could be loaded at any time. By "selections state" I mean the set of the states of all check-boxes (on both tabs--[OS] and Applications), excluding the ones that haven't been changed from their default, the exact same checkbox state information currently stored by CCleaner in the registry (on Windows) for persistence between sessions. In principle you should be able to have as many presets as you have disk space for, but obviously in practice people would only use a few, so a max of at least 10 probably wouldn't be unreasonable (in my opinion). Ideally, users would be able to load (and save) them without going into Preferences.
Consider putting a small button in the empty space to the right of the [OS] ("Mac OS X" in my case) and Applications tab labels on the Cleaner pane, that dropped down a menu containing a list of existing presets and, separated from them by a horizonal divider, a "Save as preset" that would open a prompt for a name. Existing presets would be loaded by simply clicking their name. (I've seen this kind of preset interface in at least a few other softwares, but the only one I can think of at the moment is the print options dialog for a high-end printer. )
This would address the needs of people seeking multiple "levels" of cleaning (see this topic, for example), but be more flexible and (I'd think) easier to implement--it would require fewer changes to the UI anyway. If stored in files (presumably, ini's on Windows) such presets could double as a way for users to backup their selections or transfer them between machines, at least within platform. As the number of applications and options supported by CCleaner (or winapi2.ini) grows, so would the benefit of not having to manually recreate a selection pattern.
Thoughts?