personally, i think collapsing margins is stupid. People tends to abuse using margin simply because they have no idea what they are doing, because everything they do all works. In the end, they are just taking granted of this "effect".

i don't think designer should be part of the spec, no offense, they do kool stuff, but they can't drive the technical spec on calculations, ex. 1+1=2. Well, they say, yeah, i felt right today, let's do 3. f** u.