Sounds great...I'll give you some toilet roll holders which i made into a sculpture, and you give me your HDD's
Yeah, thats not how it works.
Heres an example:
I have a spare HDD. Its only 20GB, not worth any money, yet still useful enough not to throw away.
I list it on the forums, somebody on the forums wants it and pays the shipping (or collects it off me in person).
That somebody is then encouraged to give something away, its not necessary, but if he asks for something else thats free, the person giving it away may pick someone else because he's hogging the free stuff.
It shouldn't be too hard to configure a list of users ordered based on the number of "free" items received and possibly cross-referenced by the amount of time since registering. That way, the longer you've been a member the higher up on the list you are, but once you get something, you're moved to the bottom and you start over.