As is common with any major patch day, there are a few issues. Here are a few from the forums and what I've experienced:

Instance servers are crashing on many realms.
From AV to Tempest Keep, players are having a hard time completing instances. Raiding is particularly hard hit.

It's OK to delete the Auction Sale Pending notice from your mailbox.
You will still get your cash when the new 1 hour delay is up. And, yes, everyone else seems to hate the new delay, too.

Windows resolutions and UI Scaling have been tweaked.
It's not your imagination and it also, according to Hortus, isn't a bug. Changing resolutions of the same aspect ratio will only give you a higher or lower image quality, but otherwise your view will not change. Windows are automatically resized to maintain aspect ratios and to reduce issues with stretching and distortion. If you aren't happy with the new size of your UI, turn on UI Scaling in the Video menu and adjust it accordingly.

Hopefully the instance servers will have been fixed by the time the patch is live in Europe. Sometimes it's better not being first.

I also recommend checking out the undocumented patch notes.