A few years ago, I considered myself a lot smarter than I do now. I took a year long break from school and really didn't do anything stimulating to keep my mind fresh. Even now after I've been back in school for a year and a half and have picked up hobbies like this one (programming), I still don't feel as smart. I've been doing things like word puzzles and logic games but they haven't been helping as much as I'd hoped (though they have been helping).
More to the point, what do you do, if anything, to keep your mind sharp? I imagine those of you who have real programming jobs (mine is more like script writer and SharePoint lackey) don't really need to do much to keep sharp.