The example responses they provide are correct... except when they aren't. They use heterogenous JSON in their responses (silently replacing string literals with arrays, but only for some responses, etc.). They've added error codes without updating the docs for months on end (which sort of defeats the point of an error code - what use is it if you don't know what the error means?)
The only way I'm notified of these changes is when people file bug reports with the library, and I always have to ask them to tell me the exact query that cause the error for them, because they're almost impossible to reproduce otherwise[0], and the API is so inconsistent that I can't try and manually search for similar responses that will cause the error.
On the other hand, the Twitter API is a seamless[1] way to interface with an incredibly useful and powerful product, and it's a great source of data. I just wish the developer experience were seamless.
[0] e.g. https://github.com/ChimeraCoder/anaconda/issues/82
[1] Assuming your client library works, but I can't assume that if I'm the one responsible for maintaining it!