[fooandbarify]

Depending on the other content of the page and the nature of your traffic/user data, it might make more sense to take advantage of caching by making the initial loaded resource (the HTML file) completely static and loading the bootstrapped data in a single separate request.

[jashkenas]

Yes, absolutely. If the initial HTML page is heavy, and can be cached for all users, then separate makes sense. If the initial HTML page is light, or user-specific (the usual case for a backbone app) then bootstrapping in a single HTTP request makes sense.