I just ran it again. When I have the "Unused File Extentions" deselected, it doesn't delete anything in the folder. Weird... It dosen't make sense that it doesn't work for you. Has anyone else tried it?
The extensions are rft- the main ones, and there are a couple with rfo, bak. All these are in a folder called "Default Profile". If I'm not mistaken, this gets deleted too (but I don't want to test it).
It is stored in the C:\Users\cheapherk\Documents\My Roboform Data folder (obviously, cheapherk is my username). I was surprised CCleaner totally wiped out the contents of the folder.