I must be in it, because I have rarely seen a downside to using AE. Here's the nature of my apps:
1) Extremely simple or very flattened data-model
2) Few writes, TONs of reads (I peak at 150 requests/second every day)
3) The occasional DeadlineExceededError causes me little or no headache. For some people this would be frustrating.
Also AE is awesome as a CDN. The latency is very tolerable for static assets.
