Adrian,
I've recently started work on a generic node relationship framework for drupal.
Great news! :-)
There are lots of places it's useful.
I completely agree!
Images attached to a photo album node Audio tracks attached to an audio album node Events attached to a location enabled venue node Users that have other users as buddies (when we have profiles as nodes.. an idea who's time has come) Similar functionality exists for organic groups.
I'm thinking it could also form the basis for an outliner, that may one day take over the functionality of book.module.
The hardest part is an interface which will scale well for really really big sites.
I've read Moshe's and Walkah's messages, hehehe, and I don't know about your priorities, but imho this relationship framework would be really useful. Please let me know if I can help you in some way, ok? Cheers, Emiliano.