Cash them in how? As of 1 June 2007, they can no longer be converted to miles upon request, and unless you registered for the "promo" that expired 15 Aug 2007, they will no longer convert to miles upon expiration, either. The only way to cash them in these days is to use them (and I'm guessing the OP can't use them for whatever reason, given the large number in his/her account).