I'm not a big fan of OO development. I think the OO approach is poor for readability and code comprehension. However, it does make for great black boxes. I really appreciate OO for encapsulating executable code. I recently wrote a module called ImageAPI for drupal that encapsulates Images in an object with a procedural interface for manipulating the Images stored in the objects. Later I wrote a wrapper around FFmpeg and took it a step further and replaced the procedural interface with methods.
There were a few problems this nicely encapsulated.