I have found the optimal solution to the wiki naming system question:
Solution = unique ID & optional, unique slug & optional title
The slug is used to create links and in URLs. If it exists, the title replaces the slug in link labels, headlines, etc.
This system doesn't require a slug for every page (so you can just jot down some notes into the system without bothering about naming), but without a slug you can't link easily to a page (so, later when you want to link to a note, you can go back, and give it a slug). Slugs must be unique because otherwise the planned social joins (which join pages from different users/systems via their slugs) become tricky.
Novice users can simply use slugs as if they were titles, and get slightly uncool URLs, e.g. /My+Holiday+in+%C3%96sterreich. More experienced users can assign short, hopefully more durable slugs (e.g. /holiday-2007) and an additional longer title.
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