Upgraded to Jessie yesterday (Linux polaris 3.1.0-1-amd64 #1 SMP Tue Jan 10 05:01:58 UTC 2012 x86_64 GNU/Linux).
Everything went smoothly but no visual after reboot. Ctrl-Alt-F1 access was fine and no errors were apparent in logs.
I tried changing display manager from gdm3 to lightdm, resulting in display of login screen followed by blank screen upon logging in.
Second, I tried changing monitors. That has made box usable, but there are still serious display problems (including but not limited to scrambled screen on Gnome desktop when clicking the "Show Applications" icon).
I'm going to guess that the graphics card is the culprit.