Why is this even needed. I thought scribe worked well with Dropbox :S

It (repository/not latest release) works well but for the callback to redirect the user to after the authentication.
OAuth 1.0a specifies the callback when getting the request token, but Dropbox ignores this. You have to specify the callback later in the authentication URL otherwise the user will never be redirected.

(see also #203 (comment))

And ~300 lines of code for that?

Why can't you just do:

String url = service.getAuthenticationUrl() + "callback=foobar.com";

Or something like that?

The number of lines is caused by the new DefaultApi10 and OAuth10ServiceImpl, which are modified copies of DefaultApi10a and OAuth10aServiceImpl.
Of course I can just the oauth_callback parameter to the authentication URL (which is exactly what I did first), but this would have to be done by everybody using it (and it needs to be documented). By doing it via a Api10 the user can use Dropbox the same way as the other services (and other 1.0 services out there can also easily use this Api10).

I really like scribe because of the ease of use (with the exception of the callback it just worked!) and thus have modified my copy in the above way to make Dropbox as easy to use as other services. As I usually share my modifications to open source software if they could be useful to others, I decided to create the pull request (which is really easy with GitHub) to let you (as the author of this great library) know.

Thanks a lot for the pull request.

In this case, I'd rather have a one line hacky string concatenation on the client than 300 lines of code in the library.

Sorry.