The biggest problem I had with OAuth 1 was that if you messed up anything chances are all you got back from the server was "Signature Invalid".

You're then stuck trying to find out where you had gone wrong with no guidance. The last time was due to an incorrect content type on the post. A coworker accidentally had the key and secret the wrong way around.

Both scenarios has the same error and you're often stuck groping around for a solution.