As overheard recently in the #banshee IRC channel:
<woodwizzle> Is there a way I can select all the songs in a directory? ...
<gabaug> woodwizzle: search for path:directoryname
<gabaug> that's path[colon]directoryname
<woodwizzle> ooh, thats cool
<woodwizzle> in fact that is friggin awesome
Our query support is fantastic. Try the alpha.