Quite often, I'm switching from FLdigi to CQRLog's QSO list to see if I've worked a particular station before. It's nice to be able to hit Ctrl-F to do a quick call sign filter, but it would be nicer if I could hit a key to cancel it instead of having to go to the Filter menu.  The Escape key, perhaps?  Something less obvious would work as well, as long as it's documented.