X server occasionally not starting properly after boot

Tue Jan 15 23:48:59 UTC 2008

After boot I sometimes get GDM in what looks like 640x480 or mabye 
800x600 resolution.  If I login, I get a session in the same resolution 
too.  (My normal size is 1600x1200)  Pressing Ctrl-alt-bksp fixes the 
resolution. 

Any idea what could cause this or how I can debug it?

The strange thing is, I saw this under feisty too, and this is a clean 
install of gutsy on the same machine.