This looks good. A couple of things: if you select a filter first, the search input disappears so you can't refine your search. And the url hack isn't necessary and may confuse caching, just use a standard query '?'. Otherwise I like the simplicity!
Thanks for the feedback. I will work on showing the search box on sub-pages, too. The current idea is that once you select the first "Feature" the rest in the sidebar are the only once you can use to narrow down the search.