In my WP installation (private site at the moment so no URL, sorry), the body element has class="search-no-results" even when there are results found (in this case, only one result). I'm seeing no difference between the classes on the body element when there are results vs. no results.
I've added a few filters (on thematic_create_stylesheet, thematic_postheader_postmeta and thematic_postfooter) and one action (into thematic_header) and removed the thematic_blogtitle action, but otherwise just messed with CSS.
Any ideas?