I upgraded on a whim this past Saturday. (Win 7 64 to Win 8 64). Using Cubase 6.5 as my primary DAW. I had to download the latest drivers for the Elicenser. Stylus RMX could not find its library until I put UAC at the lowest setting (I assume that this means it is disabled). I also set Cubase to "Run As Administrator."
I had some Cubase hanging, which required hard reboot of the system, something I have not had to deal with for a very, very long time. Studio One seems perfectly fine. I had to reinstall Ableton Live Lite 8 for some reason. Everything kept its registration. This includes Native Instruments, Spectrasonics, Rapture and Arturia Minimoog V (uses same Elicenser as Cubase). The Cubase hanging may have been due to using the X to close it instead of the menu as I usually do. I'll be watching it a bit more closely. So far, it's my only concern with upgrading.
I set it up to bypass the login screen: How to bypass the Windows 8 log-in screen | Microsoft - CNET News
I went through the Apps section and right-clicked my favorite programs, selecting pin to start page. With a little bit of upfront effort, I have it configured for me. I have hated the Start Menu since Vista, so I much prefer the new start page.
The pictures app is great for scrolling through all of my folders of pictures. It would be even more fun with a touch screen, but even with a mouse, it's a lot better than anything we've had before with Windows.
I still don't care for the two separate interfaces. I would have preferred that they were more bold with changing the Desktop. That said, when I'm in the Desktop, it's as if nothing signifcant has changed. I'm using File History to back up all of my libraries to a USB drive. Anything that you want backed up, you simply put into a Library. You can create new Libraries by right-clicking on the folder or drive you want to include. (i.e. you could create a library called Z:Samples that backs up the entirety of the drive).
I like the weather and maps apps. I also like that Microsoft are creating some kind of cohesive ecosystem. I didn't become fully enveloped in the Google ecosystem overnight. I started with gmail and then slowly migrated to more Google services as they became convenient. I can see this happening with Microsoft. They have the money to survive the transition.
Worth it to upgrade? I'm glad I did, with one caveat -- I remain unsure about Cubase stability.
P.S. To close full-screen apps, put your mouse pointer at the top of the screen until it becomes a hand, then pull down to the bottom of the screen. Convenient.