When you're on the client side you don't have much of a choice. On the server, there are various options. And even then, GAE is more risky than, say, .Net - si

When you're on the client side you don't have much of a choice. On the server, there are various options. And even then, GAE is more risky than, say, .Net - since you never actually buy the platform, you're subject to Google's changing prices and product priorities.