@adamkiss: Yeah, I was thinking of this solution too ... and MySQL 5.1 can do nested queries, isn't it ?
@ryan: thanx for your reply I fully understand your decision on using Adjacent model. It will surely work nice of almost all situation.
I was thinking a bit too far on what I wish I would do in the future. And I can sometime have some very very deep level.
Actually the ProcessWire semantically treat pages as "page" not as node. So after looking into the schema, I think that page can have multiple parents ?
So it's clear that Adjacent is made for It. I would be a headache to use a Nested Set.
As promoted as a jquery like API, I keeped thinking page as nodes (did you mean that ? that would be a great challenge to drupal) so I would be able to select multiples pages at once using a selector then doing a processing job on it... Per example quickly regenerate a big sitemap, creating an index access of an virtual book or sections (Some of my clients have very very big deep level).
But actually as you said, it fit the system and it completly made sens !
And is PHP 5.3 on your roadmap ?
Best regards
Nicolas BUI