OK, if you're doing MVC, then you do SEO (and improve accessibility generally, btw) by using jQuery to do progressive enhancement. So, you have your page layouts and you can render those to traditional HTML, but you can also get your controller methods to return JSON if the client asks for that in the request header.
On the page load of the initial page, you run a jQuery function to find all the links on the pages and replace them with AJAX requests for the JSON data which you can then render client-side (take a look at the new Templates plug-in for that while you're at it).
Since SE spiders don't implement Javascript, they'll get the old-style traditional HTML, as will Readers for the visually impaired.
Easy.