I like App Engine, too, however, I always worry about the "hot cache" problem (or how to call it?): if your app doesn't get a request for a while, it will be cycled out of the "active" state, and the next quest will have a long delay for booting the app again. Especially people who used Java VM languages (ie Clojure, RoR) have complained about the issue.<p>I wonder if the situation has improved in the last couple of months? One proposed solution is to have a recurring task trigger requests, but that seems like a wasteful hack. Plus, it would be unreliable as it is not known how App Engine decided internally when to "unload" an app.