I just upgraded and am having the same issues as eberhardt is describing. With constant writing, the screen flashes every 3-4 seconds. I can now see why he couldn't grade with it

Having experienced it myself now, it doesn't seem to me (as uneducated about this stuff as I am) to be a CPU issue. It seems to be a regular occurrence that happens as you write. The page refreshes, with the annotations changing from the dark black that it normally is immediately after writing to the lighter gray representing, on my device, red lines. While refreshing, it no longer displays what I am writing, though the writing does (mostly) pop up after the refresh.

Interestingly, during the refresh, if you keep writing, the lines do not appear. However, when you go to rewrite that section, they suddenly pop up. I've tried restarting, and that doesn't help the overall issue. Quick draw is on (with it off, the writing is painfully slow). I don't know what else to try... I agree with eberhardt, though... the device just got much less useful.