Just a clarification of Points Scrounger's post -
It is one dine per airline FFP per month.
So, if you and your wife both belong to, for instance, United Mileage Plus and US Airways Dividend Miles, you can score 4 dines per month by rotating your charges to CC linked to those 4 FF accounts. (Not two dines as a literal interpretation of the "one dine per airline would imply).