A little surprised
I have to say ... I did a full backup immediately before the upgrade and was very worried about games and other applications not running .. I also had some worry about devices.
My main machine was (5 years or so ago) and high end 4Ghz i7 quad with 6GB, GTX580, D2X audio, 256g SSD system drive and two 1TB data drives.
The update didn't download after a couple of weeks of the PC being left on so I forced in Windows Update. Rather worryingly after the apparent completion, Update gave the failed updated message in this article ... but everything was actually fine.
In summary ... it all went fine and is performing beautifully.
The only oddity is that some printers needed removing a re adding and my logitech webcam needed unplugging and plugging in again to get it to work even though it showed as installed ok in device manager.
My first thought was ... nothing has changed. Aside from some very subtle changes to the start / launch / status bar ... it all seemed like W7. That didn't really bother me as I was happy in the main with W7 ... but it is nice now to be current.