I had a need the other day to list directories that was empty.  This code does just that.

(gci C:\Scripts -r | ? {$_.PSIsContainer -eq $True}) | ?{$_.GetFileSystemInfos().Count -eq 0} | select FullName

(replace C:\Scripts with the root directory)
Output example:

FullName
-------
C:\Scripts\Empty
C:\Scripts\Empty Folder 2
C:\Scripts\Empty\Empty Subfolder
C:\Scripts\New Folder\Empty Subfolder Three Levels Deep