I have replaced my win7 just to try the consumer preview when it came out.(I'm still using it since I'm too lazy to reinstall everything again - to many big programs that I use for web development)
The first thing that I noticed was the boot time, a pretty big improvement compared to win7. Also the wireless takes much less time to connect.
It also uses a bit less RAM but I can't compare it to win7 since I had tons installed when I formatted.
But when it comes to video drivers, I've had some problems. I have a GMA 4500m (a bit older laptop) and the drivers that intel supply do not work with win8 (they even restricted it in the ini file - I tried manually changing the ini file but it still didn't install correctly). After looking through some older drivers I found one that didn't restrict the installer on win8 and it finally worked, but it took many hours. It still has some minor hiccups (it reminds me of win7 beta), nothing important.
Next is the METRO interface... I don't like it. It's full-screen, hard to get used to and frankly I feel like microsoft is insulting us by saying that we are too stupid for more complicated things. Sure it looks great and for a tablet it's actually pretty good but when I use a mouse and keyboard I feel like playing a game, a very bad console port. I used to work with the start menu pretty often, but now I try to avoid it. Also searching while in full-screen is really annoying, like when I want to write something that I have on my desktop and can't use copy-paste or when I want to compare things.
I've made my own Start Menu button in the task bar by putting some shortcuts that I use into a folder and then making a new toolbar

. Too bad that the search function is still in the metro interface.
So in the end? I like the improvements but I dislike metro. I'll keep using win8 for now but I don't think they can save the new interface from being completely redesigned in the next windows."Changes for the sake of changes" does not work in the IT&C world.