I'm liking it so far. Right now, I've been playing around with essential (to me) programs for compatibility, and it seems to work fine. It's already well advertised that most popular games (Steam-driven, BF4, to name a few) are experiencing no issues with compatibility. I'll be able to give a full test when I'm actually sitting down in front of the machine.
I like the start menu layout, but, I've been a fan of the Metro interface that was incorporated in Win 8. It cleans itself up quite nicely and can be organized with labels within the Start menu. I'm finding that I can store recently used applications and programs within categories as opposed to pinned to my taskbar.
File transfer seems to be the same speed as it was in Windows 7 and 8, averaging around 11-13 Mbps on a SMB share across the network, which was what I was getting before. Couldn't try this test on Windows to Windows, because my other box was down.
I seemed to be using roughly 15% less memory on boot, averaging approx 6-8 GB with Windows X, compared to 10+ when I loaded up Windows 7. This, again, is in accordance to my profile, as I do a lot of virtualization (which will be another test) upon startup. It hasn't really concerned me, as I have 48 GB of RAM.
One thing I have found that left me headscratching is that they put the resolution controls in "advanced" settings of the display properties. I'm guessing that WinX wants to automatically allow the full resolution of a monitor, probably not a wise move for the elderly folk that want a smaller resolution. And, I did encounter a bug on it, but not sure if it was due to Windows itself, or the 3rd party remote desktop application that I was using.
Overall, I'm also grateful that this is a free download/upgrade from Microsoft, which is a huge selling point for me.
For those that want to try it, and if the download is still available (can't look it up at this time) you can download the .iso for the Evaluation copy and run this with a free VM platform, like Virtualbox or Microsoft's own VirtualPC, and give it a whirl. Always recommended to do this before dumping your primary box and jumping right to Windows X blind.