I make sure the subfloor is at least 3/4" thick, then nail backerboard (1/4") every 6 inches on the entire floor. I use a mortar with a latex additive already in it, for a bit more flexibility in the mortar. Make sure to seal your grout before your first big cooking party.
jproffer said:You're leaving out some important things to consider: 1) Framing member size and spacing. 2) Material the subfloor is made of: Plywood is ok, particle board is NOT OK.
BTW, maybe I've just never read the right manufacturer's instructions, but all the ones I HAVE read say to screw the rock down with purpose made screws, not nail it. Nailing voids warranties. Also, I hope you don't mean JUST nail it down??? CBU should be set in thinset (unmodified) AND screwed down every 6 inches, trying to avoid the joists with the screws.