You know what else has a great design on a plane? The turbofan engines. In fact, give me a blueprint for a 757 and I can probably find 50,000 things with better design than the bathroom lock. I have a special fondness for the RAT:
...well, I just don't know. But no one adores the trivial like 37signals. Of course, you say, "They are focusing on user-centric design." Well...in that case, the door-light combination doesn't seem as good as a motion-detector-door-light combination, which would turn ON with motion, stay on when LOCKED, and turn off when UNLOCKED. That didn't take an engineering degree to come up with. Where's my kudos?
You're introducing unnecessary complexity into the system; instead of the lock, light, and wiring between the two we would have lock, light, motion detector, and wiring between all three. It may be trivial, but ensuring fewer failure points is good design, especially at 30 000 feet.
Don't forget the bright blue light (on Southwest anyway) that turns on by the flight deck door to let everyone else know the front lavatory is occupied. This is to prevent a line forming (in violation of TSA regulations).
The comments are better than the article -- as one notes, the design is terrible if you're not inclined to step into a tiny, dark room and lock a door behind you (e.g. a toddler who is afraid of the dark). I'm not a cranky toddler, but I've thought that this arrangement was a bit goofy, myself.
My feeling is that a better design would use a motion detector to activate the lights. The combination door lock/light switch design doesn't seem to do much of anything, other than make the door more complicated and expensive.
Don't bother detecting motion in the space in the room--just attach an accelerometer to the door. It's not going to be touched unless someone's coming in, and they'll usually start to close it before they step inside. That is, if it is closed by default. Open by default might be harder.
So when the maintenance people clean the lavatories, do they bring their equipment in and lock the door so they can see or do they cart around their own lights so they can leave the door open and have enough room to work? Or is there an override switch somewhere?
If anything, this article demonstrates the great design of reader comments - almost all of them disagree with the OP and make better reading than the original post!
http://en.wikipedia.org/wiki/Ram_air_turbine
and if I had to choose between the bathroom lock and this set of technologies,
http://en.wikipedia.org/wiki/Ice_protection_system
...well, I just don't know. But no one adores the trivial like 37signals. Of course, you say, "They are focusing on user-centric design." Well...in that case, the door-light combination doesn't seem as good as a motion-detector-door-light combination, which would turn ON with motion, stay on when LOCKED, and turn off when UNLOCKED. That didn't take an engineering degree to come up with. Where's my kudos?