Apparently this has existed since the olden days (introduced in OS 8 maybe), but I only learned it last year. In the Finder, Command-Down can be used for "open" on either folders or apps/docs, and Command-Up can be used for "open parent." Obviously this method of Finder navigation doesn't make much sense in Column view, but I use it exclusively with Icon view now. I'd be lost without it. Does anybody else actually use these keyboard commands, or am I the only one?