Assaf writes about using Hahlo and Fluid, and I find this paragraph especially interesting:
A great Web app uses persistent, readable URLs for every interesting resource. Twitter does that, so it’s pretty easy to share links to people, statuses and other points of interest. Hahlo hides the entire user interface behind a single URL, but it works extremely well because Hahlo is just a front end, Twitter is the system of record. If I need to link, I wouldn’t be using Hahlo links anyway (although link discovery is missing in the current version).
Perhaps this is a good way to both have the cake and eat it? Have a restful, share nothing API, which is accessed by a separate GUI app built in say Seaside that can use state as much as it wants.