Considering the development of money is one of the greatest events in the history of mankind, enabling goods and people to travel freely, I cannot help but think that this is a slightly backwards step! I can imagine that most of the stuff on these website are things that people really don’t want i.e. rubbish, any good stuff will go on eBay for exchangable elecronic pounds which I find useful in satisifying my consumer needs. In short, I don’t think that these sites will be challenging the eBay or the classified sites at any point soon.
It is also a bit of a mystery to me how these sites expect to make any money. Advertising perhaps?
I find a good service for getting rid of stuff which is not worth selling is freecycle.