...But you're a tech enthusiast and already knew that, right?
I'm keeping a low profile today waiting for the dust to settle. And if you're on a deadline, it's probably a good idea to wait for the furor to die down before attempting to update your production machines.
I've updated four systems so far: my Surface Pro (from Windows 8.1 RTM), my Surface RT (from 8.1 Preview), a Dell desktop (from Windows 8.1 RTM) and a custom-built desktop (from Windows 8). No problems whatsoever to report, except that the latter system required almost two hours to update.
If you're moving from Windows 8 to 8.1, remember that the installation will remove your Wacom Feel IT drivers, so you will need to reinstall those.
Intel has yet to update its HD Graphics 4000 driver to Windows 8.1, so we can assume that what installs with the OS is the latest and greatest. Programs like Mischief 1.08 which previously required a separate graphics driver update run fine under Windows 8.1.
Celsys today released a Windows 8.1 patch for Clip Studio Paint, Clip Studio Action and Clip Studio Coordinate. This is for the Japanese versions only. The English language site does not mention version 1.2.8, but I'll report back as soon as it becomes available. We can only assume that Manga Studio will be updated shortly thereafter.
If you absolutely must have the latest, greatest version now, a fan-made English translation of CSP 1.2.8 is already available here.
If you spot any issues after you update your Surface Pro or other Windows 8 system, please report it in the comments section below and we'll do our best to verify and find a fix.