It has taken me an entire day of troubleshooting, and finally completely erasing the drive and reinstalling the OS and restoring in order to get my laptop (with my whole life on it) working again.
Can I tell you how glad I am that I had made a complete backup of my drive the day before?
I've always known that you're supposed to back up, but I'm ashamed to say that for years and years I always put it off till 'later'. I've been unbelievably fortunate in that I've never had the kind of crash where losing everything was an option. When I put Leopard on my laptop, it has a great little backup program called Time Machine and I actually only started using it a month ago.
I will continue to make regular backups from now on. Religiously.