I have a weird problem. A few keyboard combinations seem to have stopped responding. Among others Option-8 and Option-9 do not work. In fact everything from Option-3 to Option-0 do not work. Option-shift-8 etc. works fine though.
I have had the problem previously on another mac (iMac, Snow Leopard, with full size keyboard) and am now experiencing it on my MacBook Air (Lion). Last time the problem solved itself via a reinstall of OS X.