Thanks for the feedback.
We use the categories field for additional customer groupings. I had initially thought of making each department a separate organization, but this does not reflect all of our customers' business models - i.e. some customers have traditional "departments" whereas others have separate business units which we already treat as separate organizations and link them to.
For simplicity I have been adding the department field on top of the Middle Name field in the Identity section. Probably not the best place to put it, but it was the easiest.
If you could add the field that would be greatly apreciated, though I am conscious of the massive amount of work you are doing on this and realise this request is probably of minor use to other users.
Cheers
Manuel