I like new website ideas. But the idea behind YouSwop is certainly not new.
Those old enough to had used the internet back in 2000 when surfingbananas and interauct were still kings of Singapore online auctions might have realized that this concept was already there in around 2001 in the form of JuzSwap. The website failed of course, because it is difficult to match wants and haves. Most importantly, the society has always preferred to use money as a mode of exchange because it allows easier transactions and matching of haves and wants.
Patronising YouSwop is like going back against time and sooner or later the users (like our ancestors) realize that the correct way to do exchange is to involve money and not merely bartering one good for another.
The concept of ensuring credibilities of users is great because it allows user to transact safely. But this do not address the most important fact that matching is difficult. Once users realize that it is difficult to find what they want (cloth sizes, etc) they leave the website. And no one visits an empty website. The spiral continues and everybody leaves.