Yeah, this is real. It has only happened to me this one time but it would be fun to see it again. At first, I only noticed the bug in the title bar of Safari's windows, but after restarting Safari, even the menu mixed up. iTunes was in the background the whole time so I don't know when it messed itself up.
I discovered the save dialog when I tried to export the file in Fireworks and decided to put a screenshot of the dialog into the original one. So that is the only part that's 'photoshopped'.
If you want more proof, I can easily brag with my uptime:
Schreibtischlampe:~ sschmidt$ uptime
1:17 up 2:14, 2 users, load averages: 0.73 0.74 0.65