I have an old XP-era Tablet PC, so it's not the BEST platform for evaluating Win8 ... but that said, I've not seen anything at all compelling in Win8 to make me want to switch -- quite the opposite. All the hardware on my Tablet works in Win7; some of it does NOT in Win8 and that can't be "fixed". I've used Metro, and while it's interesting, without a touch screen, I see no improvement in it over the Win7 desktop. One of the main improvements in win8 was supposed to be "live" Tiles -- but none of mine are Live and I've found no way to make them work. They did in Win8DP; they don't in Win8CP.
As to performance, it's no faster than is Win7 and, based on the relative difference in noise that the fan makes, it seems to be using MORE CPU cycles and running hotter. It boots no faster than Win7, and doesn't feel any faster at all.
I haven't installed any of my apps on Win8 because I don't feel like deactivating the ones I use every day on Win7 and am not going to buy another copy of each just to try Win8.
So basically, to me, Win8 is a repeat of Vista -- no real improvements and some setbacks.