Just did the upgrade now, so far I have noticed that the following was changed:
The location of my documents, videos, music, ect was reset to default. (the redirect links from my SSD to a hard drive we set to default)
Start8 doesn't work

hope they update it soon to work.
The Apps that came with Windows 8 were reinstalled.
There's new irritating Apps now, like Skydrive.
My sound driver needed to be reinstalled.
The columns in Windows media player were reset.
The link to your personal folder and Internet Explorer were put back on the taskbar.
8gadget Pack doesn't work, had to reinstall it to work again.
Customized settings for audio and recording devices were reset.
Your personal folders (documents, music, videos, downloads and desktop now show in the Computer window.
"Computer" has been renamed to "This Computer"
New Skydrive link on the left navigation plane, which I am still yet to try and remove... ah yes fantastic:
http://lifehacker.com/how-to-get-rid-of-skydrive-in-windows-8-1-explorer-1447031829
Windows Experience Index is gone, from what I can tell.
Taskmanager customized settings have been reset.
The Pc Settings App has been changed around.
The Wordwrap option in Notepad was unticked.