I had troubles with x-server when I updated Ubuntu on my wife's eee-pc. Though I did spend some time trying to track down the problem, in my opinion it takes so little time to reinstall, that it's a better option. Now I always put her files onto a USB/SD card, and that means the data is separate from the OS. If there are x-server troubles, I spend 15-20 minutes trying to fix them, but if that doesn't work, I just reinstall. Maybe I'm lazy...