The 'longhaul' module may cause instability or even hardware damage on some systems. Unfortunately, it is now being auto-loaded on all systems with a compatible CPU (VIA C3 or Cyrix III). See bug #707047.

Before upgrading one of these systems to Debian 7.0 'wheezy', if you do not currently use the 'longhaul' module, you should blacklist it by creating e.g. /etc/modprobe.d/blacklist-longhaul.conf containing the line: 

  blacklist longhaul

I would advise against attempting a fresh installation on these systems at present.