You don't really buy from Alibaba, you buy through Alibaba. The amount of money we've spent to the Alibaba owned TaoBao is getting very scary indeed. It's like eBay and Amazon combined, filled with a crappy ActiveX plugin (Alipay) to pay - usually combined with a security token from either of the four dozen or so big banks that one may be a member of - and any question you may have pre-sales answered. Or post-sales too. It's what eCommerce should be in the Western world.
To say that TaoBao is the eBay of China is under-exaggerating things by about hundred-fold.
And it's a shame no one in the Western world has heard of it. It's Alexa rank is... 14. And it's crazy to be assuming that Facebook is supposed to be worth $100 billion, but Alibaba just $35 billion. It should be the other way round.
Also, if TaoBao ever decides to launch in the US, it's game over for eBay definitely and beyond any doubt. It might survive as an exclusively craigslist kind of thing. Amazon should be able to compete, but they will lose a lot of market share.