I’ve been doing this quite a bit lately, and didn’t even realize it was a new thing until I did it in front of a friend the other day, and she said, “Woah! I didn’t know you could do that!” So, forgive me if you already know this, but give it a shot if you didn’t.
Ever try and browse through the default Open File window? The icons can be super small, especially in List View. If your eyes aren’t up to the task of figuring out just which Picture.jpg you’re looking to upload to Facebook, then give Quicklook a try..