My 2 cents:
Follow the cease and desist letter or this can happen to you:
http://www.keytlaw.com/urls/typosquatter.htm
as you can tell its very expensive. Also, you may want to drop all your other domains that use typos and mention brandnames.
It can get very expensive everytime you get sued because the new anticybersquatting law forces YOU to pay the other side's lawyer [assuming that they win]