As a guy that does tech support for a living, I can tell you that Win8 is a tech support nightmare.
Metro IE is different from Desktop IE, it's difficult to determine exactly where end users are "at" in their Windows experience (since I have to figure that out in order to provide directions to get from there to say, Manage Network Devices where I can check to see if they've a static IP, or get their network settings)
From a user standpoint... Metro just FEELS funky to me. I don't like having to shift around tiles that I never use just to find things, and I don't like having to memorize new keyboard shortcut combinations to work around an interface design choice. A user interface is supposed to make a program more user-friend and easy to use, not provide extra steps and difficulties. If using Win8 on a touchscreen, it would be quite intuitive for most people, I think, but to also force the x86 Win8 sold for computer desktops to adhere to the same paradigms used for what SHOULD HAVE been Windows 8 Touchscreen Edition? Crazy.
From a gamer standpoint... there is an upside. Though short of the faster boot times, I really don't get what it was (I obviously didn't pay too close of attention to MaximumPC's article on the subject)
I too did the $15 upgrade, and OP, thanks for the note about the Media Center extender - I'll have to snag that. Right now, I'm running Windows 7 on my laptop, and I'm debating whether I'll bother to upgrade. Either way I go, I'll be using Start8, or the freeware alternative thats more powerful but harder to use,
Classic Shell.