I second this. Linguistics and "slang" is pretty interesting in its own right. I believe that "cool" is more universally used. Usually smooth is used to describe an action that someone did, not really heard it being used in place of "cool".
I tend to agree, smooth is IME also usually (but definitely not entirely) used sarcastically, when someone does something accidentally silly, like bumping into a glass door or similar.
(under 30 male, west coast USA perspective)