Searches only certain folders, by a using a prefix, like
m bombtrack (e.g. would search for bombtrack in C:\Music, D:\Download\Music)
v insaneflick (e.g. would search insaneflick in C:\Video, D:\Video, E:\Video)
Could be anything you can customize it all:
.v v, v. v# #v or vc vd ve for single drives
Perhaps a space before the prefix would mean you're using this one. Perhaps another hotkey for opening in a folder restricted search mode. Perhaps a double tap of the normal hotkey would switch between the search modes - I guess that'd be ergonomical. Otherwise you'd have to use some prefix or postfix (for the first letter(s) only) like , # / .