"Only show available" doesn't seem to work except on the homepage... but I think it's because the homepage is the only place where any domains are actually marked as already being registered. (when most of the suggested domains on search results seem to be registered already, based on a quick sampling.)

On the same line of thought, it would be awesome (but probably difficult/expensive) if you could show the price of each domain directly in the results.

Otherwise, it seems like a neat tool!