Sometimes the best geek tips aren't something huge and revolutionary — sometimes they're "duh" things that you either forget you can do, or they're so simple you feel like you should have known but just never learned for some reason.
My "duh" geek tip is being able to use drag and drop in Google Reader to organize your feeds. I've been using the "Manage My Subscription" button ever since I've been a Reader user, and manually going to arrange and organize my feeds. I just found that you can simply drag the feed name in the right margin and drop them into new folders, and out of alphabetical order (which is the default) into whichever order you want.
Do you have any "duh" geek tips?