I've created 2 small web apps that made use of Twitter and authenticated via oauth. It's been pretty simple for the most part. Since I develop in rails, I've had the pleasure of using twitter-auth for authentication.

Generally speaking though, this is a great move by Twitter in my opinion. I'm always a bit concerned when a 3rd party website asks for a username and password. In some cases I no longer provide credentials when I know a certain service provides oauth.

It might not be as easy for non-web based applications, but I'm sure things will improve in the long run.