Screen keeps going blank

I mentioned this in previous entry (on software RAID). My screen keeps going blank. Ctrl-Alt-F1, breathe in, breathe out, Ctrl-Alt-F7 fixes it. I.e. that must reset the video card or X.

It used to happen once a day or less. Since switching to RAID it is happening once an hour roughly. But 9 times in past hour, which was past my threshold, so I went hunting...

...and came up empty-handed. Xorg.0.log has entries but they match what happens if I do the Ctrl-Alt-F1/F7 sequence. /var/log/acpid also has an entry that I think goes along with Ctrl-Alt-F7. But nothing else. No errors in either. Nothing in messages, syslog et al that could be associated.

/var/log/gdm/:0.log also gets an entry when I do ctrl-alt-F7, but nothing beyond that.

Nothing else in /var/log at all.

I'm stumped. I doubt over-heating, and I doubt CPU load (as all I've been doing the past hour is typing in a text file). w tells me "0.00 0.09 0.07".

Not a very informative blog, sorry. Anyone got any suggestions? I don't want to mess around trying different video cards, monitors, etc.; it is still just a minor irritation.

UPDATE: After updating to Ubuntu 8 I still had this problem, but worse my Ctrl-Alt-F1/F7 fix no longer worked! A bit of googling tracked down a solution:
In /etc/X11/xorg.conf, in "InputDevice" section, I commented out these three lines:

  #Option  "XkbLayout" "jp,jp"
  #Option  "XkbVariant" "latin,"
  #Option  "XkbOptions" "grp:alt_shift_toggle,grp_led:scroll"

and replaced with just:

   Option  "XkbLayout" "jp"

Even better, Ctrl-Alt-F1..F6 now give me a terminal! They never have in Ubuntu, instead they just gave me a blank screen. The above xorg.conf has been there since the start - Ubuntu 8 upgrade didn't alter it.
(Oh, and the above change has not fixed the screen going blank problem, so I'm still no closer to fixing that...)

Update: I've noticed if I move the mouse, especially the mouse wheel, just after the screen goes blank, it comes back. It doesn't always work - not sure if there are two problems here, or if I'm too slow reaching for the mouse sometimes.
Anyway, if that suggests a potential cause for someone let me know!
(By the way, I have screensaver set to blank, after 30 minutes of inactivity. Just to see if that is related I've changed screensaver to some animation, and I'll let you know!)