Would be great (& I think you could make quite a few sales!) if you could emulate the outlook-based Taglocity program to a windows explorer-based Tag program.
Utility would be awesome & current competitors in the PC world are weak and little more than half baked betas (Tag2Find, TaggedFrog, TaggTool, Tabbles).

Marketing catch phrase could be something like, "pile, don't file" and you could initiate a whole new movement.