Another interesting change is that SearchMash recognizes some classes of proper nouns and displays refinements for them. For "Britney Spears", you'll see these refinements: "songs", "albums", "lyrics", "history" and "influences". Unlike the related searches, these refinements are the same for a category, much like Google Co-op refinements. But Google only adds "songs" or "albums" to the initial query, so it doesn't use tagging like in Google Co-op. Another class of proper nouns is companies.
If you make a spelling mistake, SearchMash replaces: "Did you mean [this]" with "Did you mean [this]? Yes / No", so the suggestion becomes a real question. Also "See results for: [suggestion query]", followed by three top results for that query, becomes "Are you looking for [suggestion query]? Yes / No".
Another new thing is that SearchMash is down most of the time, so you'll have a hard time actually using Google's experiment. But if you'll be patient, you might see the future Google growing in front of your eyes.
SearchMash has a minimalistic interface that removes a lot of artificial elements and wants to integrate all the different kinds of search results into a single comprehensive page.