The addition of column headers in Snow Leopard's Open and Save dialog boxes isn't just cosmetic: Control-click on the header to access a contextual menu that lets you choose which columns will be displayed.
Once you have the columns you need, sort, rearrange, and resize them the same way as in a Finder-window list view. When you need more room in the dialog box to see all your columns, drag the bottom-right corner to resize it. These changes are application-specific, so you have to design your dialog boxes for each program; but, once you set them, they remain that way until you change them again.
