Hey there!
 
I had catastrophe happened when I updated my non-music computer from Windows 8.0 to 8.1- I lost all USB ports and had to reinstall OS and start over. This is why I am being careful with my music computer and would like to make sure everything is compatible. I have been contacting tech support of all involved manufacturers. So far Presonus and Motu reported no issues. Waiting on Native instruments, IK Multimedia, Novation, Roland, Korg and Steinberg/Yamaha.  
 
I want to update to 8.1 sooner than later, because it is better to be updated and deal with issues, than have no issues now, continue building the studio and then get issues later. The other reason is that Microsoft gives us only 2 years for the free update to Win 8.1. Also once in a while (actually- only once so far) I was not able log in to my 8.0 computer- I had a line across the screen, demanding to update, and the only way to proceed was to agree to it. It took me to the App Store, and then I was able to cancel update. All this is frustrating, so I want to update and get over with it. Please, share your update stories and issues you encountered, especially with software synth. I have almost all popular soft synths and worry that everything will fall apart. Thank you.   

I visited Roland web site, and this is what I see:
"No: No plan for compatible version- We are sorry but we have no plan to make it compatible with Windows(R) 8.1 64-bit Edition"
 
What does this supposed to mean? I paid almost $3500 for V-Synth GT and $2500 for the Fantom G, and they saying- they have no intention to make it work? Every manufacturer releasing drivers for their products. What are we expected to do- stop using it? Microsoft forcing this update. I use V-Synth GT MIDI the most (can live without audio). How much trouble would it cause if I update to Win. 8.1? What does it do? Does it crash the system, or MIDI stops working? Did anybody tested it- any chance it would work?
http://www.roland.com/sup...&id=63060593#synth
Thank you.

I can tell you that RME has had a wave of new drivers and updates to DigiCheck when their release cycle is usually slower.
 
See this thread...
http://www.rme-audio.de/forum/viewtopic.php?id=17980
 
Initially Mathias seemed to think there was some ASIO change in 8.1. I don't know if there was or wasn't, but seems like something is catching some people off guard.
 
Initially, there was DigiCheck 5.6, then 5.61 to fix the issue. Now we're on 5.62.
 
I still haven't upgraded my main DAW. I'm testing software on my daughter's laptop until I feel safe.

I'm on 8.1 x64
Sonar X3c
Toontrack Sup Drummer 2, EZKeys, EzMix 2 all software working
Native Instruments Komplete 9 Ultimate all working
IKMultimedia Amplitube 3, Arc 2, T-Racks 3 all working. 32 bit soft synths not yet tested.
iZotope, Ozone 5 Advanced, Nectar 2, Alloy 2, RX2 Advanced, Stutter edit all working group fine. All other Isotope products still to test.
Melda Productions. The complete VST 3 package is working. They're free.
All Sony's DX plugins work.

Thank you for the info. I was wondering about Komplete 9- I have Ultimate as well. I have issue with Maschine controller- it won't let Win 8.0 boot when connected. Doubt- 8.1 would fix it. Thanks for free plugins. Will look in to them.

Just upgraded from Win 8.0 to 8.1 - I tell you the upgrade process was a total **** (because I run multiple OS's and Microsoft haven't really accommodated for it well, buggy!)...No DAW software on yet... fingers crossed for later....

I'm only part way through a fresh Windows 8.1 installation and even though I've got Maschine (original) I'm sticking with software first with intensive testing before ip get to hardware.

I had problems with the preview and had to revert back, I now have the full release installed and it is running very well.  There are some changes MS made I am not that pleased with but overall it seems to be a little better in is solidity. 8 was very solid 8.1 seems even better.
 
 

John, could you name one or two of the changes you are NOT pleased with? I'm still hovering at the edge of the diving board, uncertain.

Gswitz, they are not big or show stoppers but subtle. Library folders are now hidden by default and don't work with public data. If you had them you will not see them unless you tell explorer to show them. Its more cloud oriented, I'm not. I don't care that if you add an app it is not appended to the start screen but is held in the broad overview of all programs and apps. 
 
There are a couple of other things that I can't decide whether I like them or not. So I wont mention them.