Comment # 1 on bug 1195929 from David Webb

Sorry - this may be a false report.  I should have tried restarting more than
once before sending a report.

This morning I checked again by removing the updates directory and the radeon
file before rerunning depmod and mkinitrd.  This time the computer started
without hanging up.  

However the original problem was real enough - disk activity stopped and the
screen died before the login screen was reached.  So maybe it was a one off or
something to do with the first boot after an upgrade.