Discussion in GTD on Yahoogroups about the use of piles. The seemed a silly idea till I realised that my three trays are a Pile. Why not have that stuff in a File? It needs to be in your face until it is is filed so no other reminder system is need for the day to day stuff.
It is quite profound, at the basis of such practical stuff on the surface is a major impact on the psyche, for me anyway.