Right alt key
I don't use the right alt key much and at some point in time it just stopped working. I thought the key itself was dead, though that was puzzling. Turns out Ubuntu Feisty (and possibly earlier versions--I have no idea) maps the right alt key to a third-level character input key for extended characters.
I bumped into the System -> Preferences -> Keyboard panel and also discovered I can very easily switch my caps lock key to a control key. Ahhh... happy emacs pinky....