I upgraded this weekend.
I don't mind the UI, I mean it looks nice and all, but these are my 2 issues with it.
1) The UI is useless until ALL applications are "native" to Windowss 8. If I click on an application within that UI (Windows Media Center, for example) it takes me completely out of that UI into the "classic" desktop. Then, if I want to go back into the new UI, I have to click/keyboard press to get back into it to either look at that UI, and/or launch another application from it. ...............What's the point then? Why wouldn't I just stay on the classic desktop to eliminate that 1 extra step? I'm going to have all of those shortcuts on my classic desktop, but I'm going to click back into the new UI just so I can click on the shortcut from there? What? It just doesn't work. The new UI doesn't make sense to use until ALL applications work directly inside it, and I'm not 100% sure that will ever even happen.
2) Why do I even care about all the new things that the UI adds? There's an "app" that has an actively updating tile for new emails, new IM's, calendar reminders, and status updates? Oh hey guess what? My phone that's sitting right next to me does all of those EXACT same things, and if I'm doing something on the PC, I'm betting that I will look to my phone before I go back to that UI and out of the program I'm messing with. Or my iPad.
If MS "invented" all of the functions of this UI, it would be brilliant. As it stands, they're just adding these functions to one more in a long line of places that we already utilize them. It visually looks nice, for the most part. But I'm just not seeing the point to most of it beyond "Well every device does this stuff, PC's better start doing them too."