And that is exactly what I've done on my most recent site. I see this as the best solution, since the site caters to people who are more likely to have modern browsers that support the History API, giving them rich interactions and leaving only a slim margin of viewers with a "static" version of the site.

But it would be nice to be able to degrade nicely, and still support some degree of ajax with linkable states. Beggars can't always be so choosey, I suppose.