Installed Windows 8.1 with Media Center on Surface Pro experience. I have successfully upgraded to Windows 8.1 on my Surface Pro and I thought I would post my experience with it. So first off, normally we would have to wait to get Windows 8.1 in a downloaded format but I decided to use the RTM ISO to install it now. I backed up my system using a USB hub with external drive and a bootable USB stick with Macrium Reflect Free edition on it. No other backup tool will work on the Surface Pro as far as I was able to figure out. This is because of our SecureBoot/UEFI options inside the "bios". You need to have any formatted USB stick as FAT32/64bit/GPT in my testing, and even then you need it to be a signed image. Ie; Windows Installation/Windows PE x64 Type. In the end this was all supported by Macrium not my original choice of software as that would have been Acronis. Acronis doesn't have any supported boot media yet, and I wasn't able to get the 64bit Linux boot cds to work as someone else did on my USB external disc drive. Once you have your OS backed up if you choose to do so here are some considerations. Windows 8.1 can activate with your installed key on your original 8.0 installation, you can get this product by using nirsoft's product key tool. This should be common knowledge by now but what made my circumstances different was I had added Windows Media Center on my pc. So I first needed my Windows Media Center upgrade key which I retrieved using nursoft's tool, then I created a recovery USB media device from the built in Windows Recovery partition. Once I did this I and had a good backup of my OS as I wasn't sure how things would go... I reinstalled windows using my recovery USB key. With the new fresh factory reset surface I grabbed my nirsoft tool to get my original 8.0 key and proceeded to install 8.1 from my FAT32/GPT formatted USB bootable Windows 8.1 USB install key (I choose to do this from windows instead at this rime). I used a available 8.1 install key to get 8.1 installed, Google for this key. You may be able to use your 8.0 key to install the OS but I don't think you can and didn't try. I had SecureBoot turned off at this time so I'm not sure if that made any difference, I don't think it did. Its very important that your OS USB install key be formatted FAT32, as most of the ISO to USB tools make them ntfs. I used Rufus's tool to make a USB device that was compatible with UEFI. Once 8.1 was successfully installed I noticed the video driver and a few other drivers weren't installed. I went to Google and searched for the latest driver pack by Microsoft (August) in my case, and was able to get that resolved. I turned on SecureBoot and then used my 8.0 key with "slmgr -ilk" after running "slmgr -upk". Once installed I ran "slmgr -ato" to activate and everything activated. I then used add features with my Windows Media Center 8.0 upgrade key and I then was able to install that. After all is said and done, I'm now running 8.1 on my surface pro. I realize some of this is self explained but I thought I could provide my OEM surface pro ISO upgrade experience and maybe it will help someone else that had upgraded to WMC edition. NOTES; USB Keys must be FAT32 on the Surface Pro, as UEFI doesn't support NTFS. And there is not legacy boot available for this tablet. Windows 8.1 doesn't have all the drivers for the Surface Pro, talk about odd... maybe this was something I did but I don't think so.