When you have a traditional faceted search that uses AJAX the user experience is generally good because there is immediate feedback on the current state of the system. The user will know what other facets are still available to further refine their search, and they cannot select a combination of facets that will return zero results.
The problem is how do you give the user the ability to save/share a collection of search criteria?
When using a full page post back for each selection you can add query string variables representing the search criteria, but this is not the case with async.
Option A: Include a "Permanent Link" element in the UI
Option B: Include a "Share This" element
Are there more options? Should you even try to do this?