Cross-language conversions (Score 2, Insightful)

You haven't said which programming language the SDK is in, but one thing that makes a bad SDK is one that's a literal translation from an API in a different language.

Case in point:
A Java API for a commercial product is based on the earlier C API. All the magic handles are properly translated to objects, but sometimes the internals stick out. It has a method you can (or, as it turns out: must) call to set the character encoding the library uses to communicate with the server. This makes sense for C, which needs to be told, but if all of your Java API uses Strings, a method like this is nothing more than a please don't suck method you have to call, or things fail.