To answer the original question, my clean-shaven, short-haired (according to passport photo) hubby decided to grow the mother of all beards and his hair is now halfway down his back. We've flown to several countries and yes, they do look closely at his photo and then him to make sure it's the same person, but it's never caused us a problem.

I think he might have an advantage, though, because he's always traveling with me and I can always make a light-hearted wife joke. My hair is much longer than my passport photo, too (but same colour and no beard!), so it probably seems like less of a deal when the two of us go through.