Updated 3 systems, all XFCE 64bit. A Dell 7440 laptop with no issues, a custom desktop with no issues.
However another desktop locked up during upgrade and totally froze (upgrading via pacman in terminal). Left for an 3hours and no progress so hard reset. System was then "screwed", not booting past GRUB and no access to any tty, only black display, no cursor, nothing. Fixed by editing the GRUB boot options on the "Linux" line and simply adding a "3" after quiet. (No need for chrooting).
This then booted to a terminal and i was able to recover the system simply by install the upgrade again. This time no crashing and everything install fine. Rebooted and system is good again.
Not sure if it matters but the system is a Haswell i7 with Quadro k620 GPU.
Small issue but easily fixed. Thanks for all the hard work team.