Im using them till the last day for my self since it would be cheap this way over the 1 year subscriptions.. Plus I have a few friends that would like to do this also.. Cheaper XBL + new records = happy me.
Not to rain on anyone's parade, but I thought I heard you could only do the free 2 months once. Microsoft remembers your Xbox whenever you sign up for another account and they will see you already took advantage of the free trial. Not 100% sure though, but just a warning...