I just don't think it's worth using the WMC netflix plug-in. The video quality of many of the shows and movies is also much worse than the PS3, Roku, etc. I doubt Netflix or Microsoft care about the plug-in anymore, so it's unlikely it will ever get an update.
I'm crossing my fingers that Netflix will develop a Windows 8 plugin . It's practically guaranteed for Windows 8 on ARM tablets, but I'm not sure if there will be an x86 version. Netflix and the studios like to keep their distance from the PC, probably because of fears of piracy.
I recommend just getting a Roku or some other device for Netflix. It stinks having to use multiple devices, but it's a much more pleasant experience.