I just wish more people were familiar with the way active record (in ruby on rails) handles the same kinds of issues than core data. It's so simple and yet effective in providing the solution for the most common cases. It's easy to use, it has a clutter free clean API, it uses only subclasses, no parallel-universe entities. It has easy to grasp migrations. The list goes on.

Instead of weeks and months I have spent on reading the documentation for core data, I was ready to jump right in within minutes. And using rubycocoa, active record is available at my fingertips.