Enterprise Software After-market for Excess Licenses

Halfbaked idea of the month:

A few weeks back Jeff Nolan (Venture Chronicles) and I were at a local park with the kids and between keeping them from hurting one and other we managed to discuss the software market a bit.  We were discussing software adoption blah blah blah when Jeff said something to the effect of "wouldn't it be nice if companies could resell unused seats" referring to per user software licenses.  While I haven't read an SAP software license agreement in quite a few years I'm fairly certain they are non transferable.  But I wonder if some other software agreements are transferable?  e.g. Every buy a 5 user license of QuickBooks Pro but only need 3? Why not put the other two licenses up for 'resale'.  *smiles