Yeah, I should've know.
For people that don't know:
The idea of a matrix scheme is you buy one then you have to persuade others to buy one so you can receive yours. Take the nano for example: Say I buy one for £60, then I have to persuade 4 more people to spend £60 to get mine. Then they have persuade people to spend £60... and so it continues. Well, thats the general idea anyway, there are lots of variations. But, while all this is happening the company is making about £300 (£60x5). So they make a large profit, while the consumer thinks they are making a large saving. Most of the 'Get an xbox 360 cheap' on eBay things are just links to those sites . Most people have wizened up now though luckily...
I think they are also known as pyramid schemes.