Well, I'm actually very satisfied with windows 7, I'm running a dual boot with sabayon linux and I'm very satisfied by both of them.
First of all I just love the new taskbar and the ideas they incorporated,the whole pinning and recent files thingy.
Second, network management is WAY better than other windows versions. Back when I had vista, it used to take a whole few seconds until it connected to my wireless network, right now I essentially blink and it's connected. Plus up until now I didn't find any app that I used to use on vista and won't work on 7.
As far as the system goes I'm not that sure what improvements they made except replacing DirectDraw with Direct2D, but it's fairly faster than my old windows system.Maybe the fact that I reformatted my entire hard drive had something to with it, but it definitely runs smoother and boots faster.
Anyway, like I said, I think it's pretty nice.
Also for those of you that like to play around in VMs you might find this interesting