[UPDATE] Firmware 2.01 is up; Assassin's Creed seems stable
However it appears that as well as the network issues 2.00 created, this fix also improves the stability of some games. After a serious gaming session with Assassin's Creed combined with reports from friends and colleagues, it appears nobody is experiencing the 'white screen of death' at all now.
Whether this is a global fix is yet to be seen but I can report that in the UK at least, we are no longer seeing problems with AC and other titles. Good news!
[UPDATE] After more testing and a couple of additional reports, I'm afraid to say Assassin's Creed still freezes under 2.01. There is a quick fix though - it hasn't yet frozen whilst signed in to the PSN. So before you play AC sign out and all should be well. I expect a further update by either Sony or Ubisoft will fix the issue for good in the future.