I appear to become somewhat "anal" about my PHP documentation.

Now i'm wondering if others document database usage in function headers ... for example, a fn() might read or write a database (or table thereof), or create, modify or drop a database or table. (side question: should a fn() which changes the database with "USE xxx" 'remember' the present database on entry and employ it again before exit?)

It appears in my experience this kind of factor should be recorded, but exactly how best to do this? @uses, or what?

Why don't you use @link and a listing, together with listing of assistants:

* Some comments here.
* Helper functions:
* * {@link someHelper}
* * {@link theOtherHelper}
* Reads tables:
* * {@link Table1}
* * {@link Table2}
* Reads/Writes tables:
* * {@link Table3}
* * {@link Table4}

Then you definitely have subject pages for individuals tables, without a penny but a brief description, "Holds parameters for business process X."