I was able to get my copies for $15 each back in October, installed StartIsBack (which I highly recommend) and it boots directly to the desktop, as far as performance, it's basically a bit faster than 7, mine hasn't slowed down since I installed it almost 6 mos. ago (maybe because I'm using SSDs on all my computers) and I really don't have any complains against it.
The task manager is much improved over the one from previous releases (which has basically been the same since XP), it boots much faster, it has proper support for multi core processors, and once you add StartIsBack, is basically like having 7 with all those extra features, even the start menu is exactly the same.
At first I didn't bother using the start screen and I would click on the desktop icon on every reboot, but now it boots directly to the desktop, and frankly I don't miss 7 at all.
I have installed 8 Pro on all my computers and laptops, and if you were able to take advantage of the release price (Windows 8 Pro 64 bit for $15 + Media Center for free) I think you would've got a bargain. Hell, I even got a free copy of it with my Asus wireless AC router back in December, it's like MS was giving the OS away or something...
Having said that, I would've never paid full price for the OS, and if you're happy wit Win7, I wouldn't recommend upgrading to 8 unless you find it on a sale or something.
Also, you don't have to keep your old Win7 installation in your hard drive, you can always delete it after you make sure the OS migrated all your user files and settings, I found the experience of upgrading from Win7 to 8 to be quite painless, and the installation assistant included with Win8 is very robust.
After a few weeks though I ended up nuking my OS partitions (I keep all my user files in a different partition on all my systems) and did free installations on all my PCs, as I found I had a lot of old programs previously installed on Win7 that I didn't use anymore, and it's always better to start on a clean slate with your OS.