I was hunting for a Zend SmugMug API implementation (and found a proposal at Zend, but no code...yet) and ran across a talk at MySQLConf '09 given by SmugMug CEO Don MacAskill. If you want to know some of the deep inner technical bits of the SmugMug operation, this is the video for you:
http://www.bestechvideos.com/2009/04...e-smugmug-tale
The first 11 minutes (of 37!) are super interesting, but then it gets into super deep MySql discussion, and unless you are having a salacious love affair with MySql, you may have to go get a drink like I did.
It gives me a great deal of confidence in their operation, for sure. They have lost no data in the entire history of the business.