There's no real lock-in as long as you cushion your application code from their APIs and infrastructure reasonably well. I was worried about lock-in myself with

There's no real lock-in as long as you cushion your application code from their APIs and infrastructure reasonably well. I was worried about lock-in myself with a side-project I took on a year ago. I decided to go with with GAE despite experience with raw AWS, just because I was a one-man-team about an hour a day, and didn't have time for all the technical overhead. But I made sure that I could switch to more flexible hosting without much difficulty. Their Datastore might be the hardest to abstract away if you rely on it too much, so I wrapped it inside a non-queryable blob API that could really have any kind of backend to it.