Well, when I tried the preview, I found it annoying to find myself being dumped into metro interface every so often. Like some system settings were only avaiable in metro, while others were in the traditional control panel. Yes it felt a bit more responsive than Win7, but not enough to make me want to go through the hassle of upgrading. If I was assured that I could totally turn off metro and never have to deal with it, then maybe. Otherwise, the constant UI switching is just too annoying.
I didn't like Win8 at first, either. After a couple of hours, I was panning it left and right. I still gave it a couple of weeks though, just because I didn't feel like rolling back to Win7 right away. Once I started getting the feel for it, I began appreciating some of the new things, and actually grew to like it.
Like the start menu being relegated to a hot corner. It seems dumb at first. Why take away the start orb just to move it slightly left and down and make it invisible? First off, the far corner is basically an infinite space. You can hit it without even thinking about it. Just slam your cursor down there, hit the left mouse button, and there you are. Plus it means the desktop behaves the same way as the Metro apps. You don't get to the Start menu differently from the desktop than you do the twitter app. It's all done the same way.
The charms? Eh. They're alright. Once you get used to the gesture to bring them up, it's no big deal (though I hear they're still hard to hit on dual screen setups). They do offer some nice features that are just a swipe away, so I ended up kinda liking them.
Then there's the Start menu itself. I probably took to it a little easier than others because I barely used the old Start menu. It was there to shut down my computer, shortcuts to rarely used but still nice to have around programs, or do type to searches. The new menu does the exact same thing, only now I can fit tons more on the screen, and organize it better. Type to searches are better for the same reason, too. More on the screen, easier to look through (though I do wish they had an "all" default when searching, instead of taking you directly to apps first, then forcing you to click to look through settings and files). It's a "your mileage may vary" type situation, but I don't find it to be the complete ruination of everything that is Windows like the naysayers are claiming. It's different, sure. But I find it a little better overall.
Course not everything is perfect. There are some goofy, goofy, goofy ass decisions MS made as far as the UI is concerned. Like doing a big marquee select on the desktop, and finding yourself accidentally "grabbing" the desktop window. Or how the Windows key doesn't cycle between the start menu and the desktop, but rather the start menu and the last used app. Or, like I said above, the lack of an "all" dialog box when searching. Pretty dumb stuff.
But anyway, blah blah blah. Long story short, it's not half bad. It's faster, smoother, and sleeker (for the most part). I wouldn't say it's a huge improvement over 7, but for $40, it's worth the upgrade.
I'm already using all Apple hardware anyway, but I've been using bootcamp to run Win7 because I do like Win7. But I'm heavily invested in the iOS ecosystem, and the more Apple integrates iOS with OS X, the more attractive that gets.