I have a lot of functional but unwanted computer equipment sitting around that I'd rather give to someone else than throw away. So do a lot of other people. Some sort of Canterbury-localised web site allowing me to advertise the fact would be useful. More interesting: emphasise the "swap" part of this -- I register interest in some item of X's, X registers interest in one of mine, and the system tells us both so that we can swap.
The global freecycle project pretty much has this area covered now; I've recently disposed of a lot of equipment through our local freecycle lists.