What's a Mid-Century Modern Home?

I'm interested in knowing more about what Mercer Island Patch readers know about these "MCM" homes- a number of which come on Sale. I'm often asked to evaluate these before a possible purchase as to how they may be updated and/or adapted to fit the prospective buyers own particular needs.

The "Earnest Money" might well contain wording like this: "Subject to the Approval of Jerry Gropp architect AIA".

So, what do you know about your home?