[reid]

No. Those features should not be in the HTML markup if they are bonuses that require JavaScript. At least, they must be hidden until its script loads. But you shouldn't have to hide everything.

I'm pretty happy browsers don't show a big "Loading..." message until everything is loaded instead of painting the page as soon as possible. Shouldn't we be avoiding that too?

The bulk of that interface can be progressively enhanced.

For example, the message list and side navigation can be normal links. When JS comes along, they get actions (show this view, show this message) that override the default actions of those links (navigate to the page /message_view?id=foo).

If you try to use them in those first few seconds, they act as normal links-- they aren't broken, they just weren't enhanced yet. You can start using the page faster.