I've been using Win7 for a couple of weeks now. Switching from XP to win7 just blows my mind. It's great to look at it and still has the software equivalent of the "new car smell"
A lot of the gripes mentioned here can be fixed by changing the default behavior. I'm still getting used to the fact that Win7 has more clickable areas (breadcrumbs cutting out the 'Up' button, links cutting out control panel icons and so forth). I also like the new start bar, but I won't have a fair assessment till I start working on win7 (still use XP for work, but switching gradually).
UAC does piss me off though, it would have been awesome if you could add exceptions to it. UAC gives me warnings everytime my system starts up because I have Everything search as a startup item. I'm probably going to have to turn it off. Other than that, everything is hunky dory
backspace goes 'back' (which can sometimes be 'back' depending on the path you took). If you want to go 'up' just use the breadcrumb.