Interesting piece Paul.
I agree that urls can be important for users as a navigation aid or ‘escape route’ as you put it. I think the best way to help users with urls is to let them reflect the navigation. If the navigation element says ‘work’ and from there the sub-navigation says ‘project 1’, then let the url be /work/project-1/.
I think this approach makes it much easier for users to edit the urls usefully or use them as signposts as there is a direct correlation with what is on the page.
Sentenced urls like the ones on Clearleft look cool and exude confidence and maybe that’s enough to justify their use but I’m not sure they add any other value.