You might recall that after Windows 8’s launch, Microsoft gave away free Media Center product keys for use with Windows 8 Pro. The promotion ended at the end of January, and Microsoft implied that the keys needed to be used immediately or they would expire.
Here it is, 40 days later, and I just had an opportunity to put that question to the test.
In preparation for a review, I upgraded a Windows 8 PC to Windows 8 Pro and then used a free Media Center Pack key that I received from that same promotion.
The Upgrade Assistant recognized it as a working key and performed the upgrade normally. After rebooting, the system wasn’t activated, but following the link to activate manually worked. Online, no phone call required, took about 10 seconds.
That’s a single data point. Anyone else tried lately?
Ed Bott (@ wordpress.com) 
I, too, had the same experience.
I just tried my code on a new install of Windows 8. It accepted my key as valid, and after a reboot it told me, “Thanks, you’re all done and your PC is ready to go.”
I used the same key on separate computers. Does it invalidate first one? Other computer in another state so I cannot check at the present time.
Not sure why anyone needs WMC!! One of the first things I did with a Windows 7 install was uninstall WMC, so good riddance. I prefer Hauppauge WInTV software better and TitanTV for Scheduling and Recording, although I rarely watch TV these days anyway.
Even if you don’t use Media Center, this is the only way to get DVD/MPEG2 playback codecs from Microsoft. (You can also get them via third-party software.)