How does one tell a good design from a bad? It's not always apparent. If you can add new features a year later without whining about how crappy the code is, you probably have design that isn't horrible. If the code base can survive for 5 years or so, and still be readily maintainable, it was probably a good design to begin with. If the code can transition to different platforms without major rewrites all over the place, it's probably not too bad.

I suppose good designs are as Rehnquist said, kinda like porn — hard to quantify, but you know them when you see them. The real test is in their durability over the years. If the maintenance programmers are always whining about crap and wanting to rewrite stuff, you probably don't have a good design. In fact you may not even have an actual design, rather just a collection of code blobs stitched together with bubble gum and bailing wire.