I was on Ubuntu 12.4 LTS. Couple of days ago updated my father-in-law's machine to 13.10 and everything looked good so I figured I'd do mine.

Freaking video driver stopped working. Took two days of after-work time to get it working again. Really frustrating trying to debug/troubleshoot the machine I'm on when the problem is that it won't load a GUI. Yeah, I know the actual tools are command line, but I need a browser to look up the diagnosis online.

When the terminal was the target, things were formatted for that. A modern webpage is ... I was about to write "somewhat readable in a terminal" but that's not really true. So much context is conveyed via indentation, color, borders, etc. that trying to read a long comment thread without those cues is too painful.