Would it be sensible to search folders only (not files) if the first char of the input string is \ (backslash)? I found this one easier to type, and intuitive once you think twice.
Since currently backslash is used as suffix of word to indicate part of parent folder, the first char indicates nothing, thus it would be great to use it as an indicator to search folders only.
P.S. other way to switch on folder only search would (and should?) exist, but I think this one less obtrusive (easy to type).