I’ll be buying my next pair of glasses online

Over the years I've seen a lot of posts about buying prescription glasses online. The latest is this one, Matt Haughey's account over at 43 Folders. It has helpful notes on what measurements you need and a liberating result: instead of ordering one cheap pair, order five cheap pairs in different styles! As he points out, after a lifetime of wearing one pair of glasses every day for two years, having a choice of frames each day... wow. I can't wait. Anyone have any experiences to pass on? Anything I should watch out for? Besides the wrath of my eye doctor?