This may be a resolution to your problem =)
When restarting, hold down CONTROL OPTION P R. Wait until the third chime, then let go of the keys.
That will reset PRAM which may hold the the screen resolution setting on reboot.
I know it's been long time since this thread begun, but I want/need to revive it because I'm still having the same problem even after the PRAM reset (I even reinstalled the whole system but problems persists).
I guess this might be somehow related to connecting an external screen to it, because that's when I begun notice this problem.
I'm using a MacBook Pro 1,1 (first generation), running OS 10.5 now, but problem begun under 10.4. In fact there actually TWO problems
1. the one mentioned by SJTrance (very low resolution, usually when coming back from sleep);
2. good appearance but somewhat funny horizontal resolution (all look perfect on the screen but when I try to use "exposé" I realize that the edge of the "virtual screen" is not at the corner of my computer's "physical screen", but farther.) This usually happens on a fresh boot / restart.
The first problem is solved simply by hitting fn+F7, which makes the screen resolution come back to normal settings.
But to the second problem, the only solution I was able to find, so far, is open the system preferences and, under "screen resolution", hit the "detect screen" button. It flashes once or twice and the 1440x900 comes back in place.
But I would really appreciate not having to go through this each time I start/reboot my computer.
PS: I might say I'm doing a triple boot with W7 beta and Ubuntu 8.10 and I haven't had any related problems with those OSs...