ADoes anyone use buttermilk instead of water in box mixes?

It depends on the flavor of the cake.  In chocolate it would most likely be fine.  However probably not so good in white or yellow cake. (*although come to think of it, buttermilk is used in scratch Italian cream cakes.)  ...?

AI don't use box mixes, but I use buttermilk in almost all my cakes. It's actually one of the 'must do' things that makes a really great white cake in my opinion. It doesn't actually taste of buttermilk, just bliss the flavour and adds the slightest 'tang'.

I guess buttermilk is the best option. I always take buttermilk in all my cakes.

AThanks for all your replys, very helpful!