I'm a nurse working all over the USA in very busy ICU's.  While there are tons of opinions and fads regarding supportive shoes, I feel Birkenstock really does live up to the hype, and are worth the investment.  I wear the London clog, for everyday use in the fall and winter.  And then at work I wear the Boston clogs.
I'm in my early 30's and after being a nurse for several years, find these shoes work best for me and my feet.  I notice I don't ache as much after a 12-13 hour shift.

Word to the wise = BREAK THESE IN SLOWLY!

I cannot emphasize this enough with any Birkenstock shoe/sandal....you have to start off gently or you will kill your feet.  Wear them the first day for 5-10 minutes. The second day 30min-1 hour around the house etc., etc.  I've noticed that folks who throw them on like tennis shoes complain bitterly after the first time wearing them.
They are like Dansko's, in that their not for everyone but if you understand the product I think you'll end up loving them.