Me too! Exactly same symptoms, including the SIM pin prompt with messed up font (all digits appear as little squares). If I leave it, it reboots whether I put the pin in or not, but I have had it show an empty home screen (b/g but not even a status bar yet) when I've tried entering the pin quickly after the prompt comes up.

Will try flashing - not done it before, ota upgrades 'just worked' for both the previous upgrades.
Now wondering if can do that from a Linux desktop (or one without a working X server - my lucid lynx upgrade broke it; really not my week is it ). Will look...

Did do some root->/opt clearing though 1st, wouldn't install on the 30Mb I had left. It worked at 42Mb, I don't know how much