A couple years old, but still useful. Some basic ideas about how to use Smart Mailboxes in Mail.app from Merlin Mann, who tends to be pretty good at that sort of stuff.
Cheat sheet for typing accent letters in Spanish on a Mac.
Dave Winer’s Flickr-to-screensaver app. Apparently there are other programs that get this job done, too.
I should really take some time to learn how to use applications like this in ways that save time in the long run. I should, but will I? Eh. Maybe you will.