Press Cmd+Shift+S to open a search panel. Click the dropdown menu (top left) and select "Send searches here". Now enter some text in the search box and hit enter. Click on a result or two, browse around, have a good time. Now, press Cmd+Shift+S, hoping to get the focus returned to the search-box's textfield (and, have the current search text selected so that I can just start typing a new search and hit enter). No such luck. Not sure where the focus is but it surely isn't in the search panel's text field.
This has been reported before so perhaps it just hasn't been fixed yet in the current beta.