Me too. I just sent them a note reminding them that a) Imus was fired for less, b) it's NEVER funny to joke about statutory rape, and c) demanding either Letterman's firing or, at minimum, an on air apology.
I also mentioned that I'd boycott all of CBS' advertisers until c) happened.
I could be mistaken, but IIRC, Imus was employed by CBS Corporation as well (CBS Radio).
How CBS can allow Letterman to go unpunished, yet fire Imus for something far less offensive is beyond me.