But if you need the reliability and scalability that App Engine provides, I still think it's cost effective compared to attempting to build the same functionali

But if you need the reliability and scalability that App Engine provides, I still think it's cost effective compared to attempting to build the same functionality yourself. You get the benefit of directly using the work of Google's top flight App Engine programmers (e.g., Guido van Rossum). By way of comparison, I've done quite a bit of work w/ the AWS components (e.g. EC2, S3, SQS) that in theory allow you to build a highly reliable, highly scalable site but in practice there's still a lot of assembly required, whereas w/ App Engine that's provided out of the box.