[wpietri]

Depends on what sort of API you mean. Internal ones are fine, so I suppose you're talking about public APIs. Which again are fine on the client side; it's just the server that can be harder.

But I still think the way to good public server APIs isn't to sit in one's arctic Fortress of Architecture and think real hard. I think you just build and iterate in private, refactoring as you go, and then switch to a closed beta. And of course build your protocol in such a way that it's reasonably extensible.

Up-front planing is still no panacea. You will have to change your protocol someday. Someday soon if you're up to something interesting, because the world doesn't stand still. And even if it does, your competitors won't.