It's a nice to have, but other than the fact that we all used to use a dict when we really wanted a set before set existed, I'm not sure the connection is there to a layperson.

A mapping and a set type really don't have much to do with each other other than implementation -- anyone that isn't familiar with python C code, or hash tables in general, wouldn't likely have any expectation of them having anything to do with each other.

-CHB