If you put your Desktop folder inside your Documents folder and then make an alias pointing to it (also named "Desktop") in your Home directory, hitting Command-D while in open/save dialog puts you right INSIDE your Documents folder. This has been a great time saver for me. Especially since I've been pressing Command-D in open/save dialogs for as long as I can remember.
There's also handy little menu extra called Deviant that will map your desktop folder to an alternate folder of your choice. The alias route was my choice since I only wanted this one option and don't need yet another extra in the menu bar.
[robg adds: I haven't tried this myself yet, but I'm not aware of any downsides to arranging things in this manner ... although I'm not sure what would happen if you then put an alias of your Documents folder on your desktop!]

