Some things I gathered from reading on the Chinese forums:
*The OP on the Chinese forums warns that this is a buggy release, and users should wait for a more stable version to appear.
*This version is MIUI 2.1.13, which is
ICS not ICS (my bad, I think it's 2.3.7 based).
3GC101:
*There is a bug concerning the reception of MMS messaging.
*There is a bug where the SMS notification sound cannot be muted, and will continue ringing until the phone has been powered down. I kid you not: "收完短信以后听筒滴滴响,除非关机,否则关不掉。"
*There is a bug where the camera aspect ratio is incorrect.
*There is a bug where the power button must be pressed multiple times in order to wake the screen. A proposed workaround is to use volume buttons to wake.
*There is a bug where changing the default ringtone causes the phone not to ring when receiving a phone call.
*There are still bluetooth issues (very unspecific) with the 3GC101.
*A poster managed to black out his screen adjusting his brightness settings, and now has no way of making his screen visible again because he can't see his menus.
3GW101:
*A 3GW101 user reported that after he installed three apps, within half an hour his phone was unable to place calls, he was unable to end calls using his phone, and had to wait half an hour after booting in order to place calls.
*There is a bug where changing the default ringtone causes the phone not to ring when receiving a phone call.
A poster on their forums claims it is "90% perfect"... I would stay away from this one. Besides, the OP says a bug fix release is in the works.
3GW100:
According to this thread:
MIUI chita 3gw100????????-???Phone_???pad -
The 3GW100 version is severely buggy to the point of brokenness, so no dice for me.