Philipp is absolutely right, guessing a photo from among 250,000,000 is easier than guessing a photo from a GUID. It’s still very difficult. I wish I’d done GUIDs when we first started, but to be honest, I just didn’t know what they were. That’s my fault. As I explained to Philipp, we’re willing to overhaul our system to use GUIDs – a very expensive proposition – except that no-one has ever asked for them, to my knowledge, in the 5 years we’ve been in business.

That’s from Don MacAskill, the CEO of smugmug, in response to this article via Chris Shiflett.