Finally saw my very first Windows Phone yesterday at the local China Unicom store, a Nokia Lumia 800. It's very nice and the Metro UI seemed very smooth and polished. However it's also extremely expensive at a whopping 4000 RMB, that's about $600 USD, with a rather stuff mandatory two year contract. So it's priced roughly about the same as the 16GB iPhone 4S, which makes me think it's extremely overpriced for what you get. The iPhone is very overpriced in China as well, however Apple products are always popular the affluent brand-whore crowd. unlike Nokia or Microsoft.
It's very difficult to see who's actually going to buy the pricey WinPhone Nokias over iPhones, or the absolute plethora of Android phones available here. Thing is here in China, Apple has a perceived desirable lux brand cachet, like Louis Vuitton, Gucci, Prada, Armani, etc. Nokia on the other hand is probably much more associated with cheap candybar dumb phones here.
BTW no Facebook integration of course, instead the Chinese version of WinPhone 7.5 appears to have Weibo and Q-Zones integration, these were on the Metro IU panels.