Despite my early misgivings, and barring any future glaring issues that may crop up aside from not having window title bar "focus" change colors as in prior versions of windows, the download, installation and updates have gone without a hitch on a previously two year old windows 8.1 installation. (Well, basically two year old. There have been numerous reinstallations of Acronis True Image disk images after testing one thing or another fubared the system)
There were no driver issues. No problems with network attached storage drives. No GPU card problems. Nothing to resolve with connectivity. Nothing. Pretty boring actually. Aside from not liking the Edge browser and it's constantly hanging up (IE, FF and Chrome all working normally) and the lack of a colored title bar with current window focus behaviors, it's pretty much uneventful.
The biggest problem is that I don't really see that anything is different. Memory usage, benchmarks and the "feel" of the OS overall speed and stability seem to be markedly unchanged. I'm not even sure there was a good reason to upgrade, aside from Microsoft annoying the hell out of me with the reminder icon in my taskbar. At least that's gone.
System is an AMD FX platform, 990FX board, OS installed on SSD and overclocked to 4.5Ghz. Unlike some users indicated previously, I've seen no issues with overclock behavior acting abnormally and in fact one thing I have noticed which seems improved is wake response from sleep. Previously my fans would come on, stutter momentarily, shut off and then return to normal behavior. Now they simply power back up with no hesitation. I'm not sure if that's even related, but maybe worth mentioning.