Your plugin is excellent! We are testing the most recent version with its IPTC/EXIF import features with the goal of creating a stock photo site built on WordPress, and so far it is working well. Your plugin not only enables core keywording functionality, but is a huge timesaver now that tags/keywords can be imported from the IPTC metadata of images.
What is the most feasible way for us to configure additional custom fields to the "Edit Media" screens within the Assistant so that they're accessible to all uploaded media items? For example, we'd like to configure a "Model Release" field (or series of fields) attached to each photo. Ideally we'd like to configure custom fields that are a bit more complex than Name/Value pairs -- for example "Model Release" might have values of Yes, No, Not applicable, and a short 'notes' field. Currently we'd have to configure a custom field(s) for each media item individually.
We're a bit reluctant to dive in too deeply with customization of the plugin because we're not 100% sure how these customizations will be affected by future updates of your plugin or of WordPress itself.