Hmmmmm.
I work professionally, 10 hours plus a day in Windows 8. I've found that my productivity has remained the same, no better or no worse. I have set up the 'start screen' as a glorified version of the classic 'start menu' and have gotten very quick at navigating between both UIs. I'm probably faster in the new 'start screen' versus the 'start menu' because I feel it's easier to locate my applications due to the large, graphic intensive icons rather than having to study a huge scrolling list of application names.
Since switching to Windows 8 I've found I enjoy using Metro apps whenever I can. I use the 'I Heart Radio' and 'YouTube' apps every day and I'm constantly looking for apps that can replace my browser based computing. Since downloading the newest 'Office' suite I've come to love the Metro look and feel that Microsoft gave the software. I can't help it, I'm a minimalist at heart and I love the simplified, Metro styling. I wish Adobe would redesign their look and feel based upon the minimalistic, Metro style.
As far as working full screen I've been trying to use my day to day apps in full screen mode as much as I can. It took some getting used to as we'll as a comprehensive task bar menu to accomplish a full screen work flow but it was achievable and really not that much of a hassle if using an open mind. I've been doing this because I'm betting that at some point in the future, most software applications will be full screen only.
All in all, I've come to love Windows 8 and I hope Microsoft continues to refine and enhance it. I also hope that Adobe will continue to embrace their lean and mean apps like 'Ideas' and 'Touch' and trim the fat from their flagship programs.
FYI, I am a professional web developer and designer. I also create fine art using Photoshop, Illustrator and various programs on my iPad. In a nutshell, my computers are more tools then they are toys. I rely on my computer and it's operating system to earn a living.