Believe it or not, this feature was always hiding in the code, but I never really taught anyone the magic trick to using it. My main problem with not releasing it to the public was that I couldn't decide on the best place to present it on the site.
Thanks to your request, I forced myself to make up my mind. I decided to make it an option on the main search
page. Use the "Save Preference" form on the top of that page to save your preference on your computer. Once that is done, any search you execute from that page will have this setting applied to the result pages. Furthremore, browsing sections by using the main menu (Puzzle Database > Browse) will also use this saved preference.
Hopefully this is a good enough solution. I really don't want to add it to the search result pages themselves in spite of this being the current internet standard. Further, I understand that cookies aren't the best solution either since some people disable them, while other people use more than one computer to browse this site. But my thoughts were that excluding those few people beats the rest of us having to enter our preference each time we search.
Please let me know if you're happy or unhappy with it.