I love it when I discover something in the Mac interface that’s probably been lurking there for almost ever, and I just didn’t realize it. I don’t even know what prompted me to try this, but the spirit moved me and now I have another trick in my arsenal.
You’re in an Open dialog and you’ve selected something in the list—but is that the item you really want? You’d rather move to the Finder and peruse the folder the item’s in. It’s in a deeply nested folder, though, and you’ll have to do some digging. Or not: with an item selected, press Command-R (mnemonic: “Reveal”) and you’re moved to the Finder with the item’s folder opened.