some suggestions (you asked!):
1) i can't imagine too many cases of wanting to apply different masks in different directories, so having to specify same dirs for each mask seems really painful. better to just have a single list of dirs i think.
2) and then a list of masks (with checkboxes to let you temporarily disable each?)
3) the ability to drag and drop folders (or a shell extension) to scan a folder (and children) would be to me my #1 request, especially for testing purposes.
4) i think it pays to explain more about how DCS integrates into Windows Disk Cleanup and how to use Windows Disk Cleanup; it's not something i am familiar with and i bet im not alone, and its one of the unique features about this app that people might like.
5) results might also be a candidate for not putting each dif mask on its own tab (have to check each tab to see whats scheduled for deletion might be a bit cumbersome).
just some ideas - feel free to ignore