After reading Patrick's latest entry regarding Cascading LOVs in Apex 4.0 EA2, it reminded me of one of the things I used to do quite regularly in Forms - repopulate one Select List based on the selection of another, during when-list-changed.
Oracle writes in their Application Tools Statement of Direction that (in context of migration tools)
Instead, Oracle’s strategy is to provide a Java EE development environment exposing similar concepts as Forms and Reports, giving to Forms and Reports developers the opportunity to become productive in a new, but familiar environment
I think this cascading LOV is another example of that.
I defined my first Select List as an LOV with the following select:
select name d, org_id r
where parent_org_id is null
order by 1
Then in the definition for the second Select List, I designate the Cascading LOV Parent Item, and refer to that item value within my second LOV definition.