I just sent a guy home to backup his system because his 500gb 7200 RPM HD just failed on his new unibody MBP. I got Norton Disk Doctor to rebuild the directory and Disk Utility to verify it all. It will not at all boot into OS X. It will mount normally in target disk mode, but will not at all, get past the Apple logo on startup. I wonder what the odds are this issue having an effect on that.
I'm not surprised it won't startup if you used Norton Disk Doctor on it, that software was discontinued before 10.3. It used to break filesystems all the time even before it was discontinued. Running DiskWarrior on the drive might be able to fix it.
I have a late 2008 MacBook Pro, with a Hitachi 7200RPM drive. My MacBook does make the drive park its heads very often, even with a slight nudge, or with certain sounds. The iChat received message sound tends to park the heads too. Maybe Apple is going to make the sensor less sensitive, so it won't park the heads at the slightest movement or vibration...