I loved Daring Fireball’s one-line description: “So much for the lock-in argument.” There’s definitely still a concern if/when people find themselves addicted to the services Google provides beyond simple app hosting — as Andy writes:
The App Engine SDK doesn’t use BigTable for its datastore, instead relying on a simple flat file on a single server. This means issues with performance and no scalabity to speak of, but for apps with limited resource needs, something as simple as AppDrop would work fine.
Seems to me that this is where Google should head: getting developers addicted to all the services Google engineers already enjoy. They’ve started down that road and that seems to be the best approach for making App Engine competitively distinct.