I live in China and use an HTC Desire. My experience has been that you can get Android Market to work, but you have to be willing to put in the time and effort to hack your phone, by rooting it.
Currently Android Market is not officially supported in China, so you don't get access to everything in the market, until you root your phone and install something called Market Enabler.
When you first get your phone, you'll be able to access a lot of the Android Market apps, but not all of them. I'm not sure what the criteria is for deciding what you have access to here (none of the paid ones are accessible, and also some of the free ones)
You can check whether you have full access by opening the "Market" application on the phone and searching for the application "google maps" or the music player "doubletwist". If you don't have full market access, neither of them even show up in a search until you use Market Enabler to trick the system to label your phone as a phone from the US or EU.
You can download an app called App Installer from the market (even the gimped China version of the market). Then you can download the file for Market Enabler here:
Downloads - market-enabler - Project Hosting on Google Code
Put the file for Market Enabler on your phone's SD card and run App Installer to install it. Go into Market Enabler, choose a phone you want to copy from the list (I copied the US T-Mobile Desire) by pressing and holding on the entry till you get the option to "fake this carrier".
I'm pretty sure you'll have to root your phone first to do this, because often you can't install non-market applications without rooting.
You can check whether or not you'll need to root before you buy the phone though. On the phone, go to Settings/Applications. If there's an entry in there that says "Unknown Sources" with a checkbox next to it, you're in luck and you can get market access by following the above instructions without rooting. If it's not there, you'll have to figure out how to root. If that's the case, meet your new best friend xda developers forums, in particular, this page
[HOWTO] [REF] [FAQ] [Guides] [Tutorials] Flash/Root/ADB/ROM [MUST READ!] - xda-developers
Bottom line is, if you're not very technically inclined, don't get an Android phone in China because you basically have to hack it, which ends up being a pretty time-consuming process. I've written such a long post about this because it's pretty annoying to buy your phone without any carrier subsidies and still find the phone has been gimped. I'm very happy with my android phone now, but it took a long time to get there.
Personally, I'd recommend waiting till Google launches it's own version of the Galaxy S, called the Nexus S in a few weeks, which won't have Samsung's crap Touchwiz UI and will get all the Android updates as soon as they're released. Either that, or pick up an iPhone 4.