While I like the idea, it doesn't really work. I tested it on Opera 8.5 where I didn't even see the scrollbars, didn't see the values for the second dropdown.
It worked in Firefox and Konqueror, but had problems with highlighting when hovering the items. Further, it can't be used with the keyboard.
As I said: I like the idea and would vote +1 for it if it worked.
PS: Pepr doesn't allow to give me a 0 and comments...