Maybe this has been posted before, but a string in the latest Ubuntu update descriptions was triggering a crash of the X server (see thread here
It turns out that this problem was known earlier, and is reproduceable. See this bug in the Ubuntu bug database
I've reproduced this using the method described in that bug, which is:
- Surf to http://www.floriansprogramme.de.vu/tmp/crashGTK01.txt
- Copy & paste the text into gedit
- Select the text up to and including the last line
- Press backspace
Sometimes this does not crash the server, but pressing control-Z after that usually does.
I am attaching a nvidia-bug-report.log to this post, made after the crash by using the /var/log/Xorg.0.log.old file. Hopefully it is of some use.