Glad you got it working. Yes, it's confusing at first. But once you realize you can use any combination of plugins and scripts to get whatever you want...
Here's an idea. Imagine a configuration table, with data elements (chunks of data available from external sources) listed in the left-hand column, followed by a column for each external source (i.e., for each plugin or script installed), and a right hand column for setting the standard or custom field to save that data in. In each valid cell (i.e., the data element exists at the source) is a flag for the overwrite setting (omit, save if field is empty, add to existing, and overwrite). Then it would be easy to configure things like "Put IMDb user comments in Description, but overwrite this with the allmovies synopsis, if one exists." This would also provide a way to see at-a-glance where all the movie information is coming from.
There you go, nostra—something for your version 2.0 todo list. Right. I know, "...with a low priority."