Private Fields for nodes/entities

Has anyone come across a module that gives content editors an option make certain fields private?

There is a http://drupal.org/project/user_field_privacy module that has exactly the UI needed, but can only be applied to fields in user entities, and I'm looking for something that can be applied to custom bundles ('Content types' - essentially nodes).

There was a D6 module for CCK Field Privacy which has a poor D7 port, but the UX for this is very complicated (setting up buddy lists etc). D7 Field Permissions module has the ability to set fields to public or private, but this is for an entire Content Type, rather than configurable for a specific instance.

I'm trying to work through the User Field Privacy module to make a custom module, but there are a lot of hacks based on the UID that don't quite translate for a NID.

So grateful for any suggestions, or if anyone has come across something that may help.

Happy Friday.