Shortcut Key for don't save in save dialog. It should respond to Command + D.

I'm using the standard dialogs that are provided by the system. I don't think I can change that behavior.

Thanks for that information.
It looks like it is an OS level change that has caused the behaviour change, as of 10.6.8. 

For Lion and Mountain Lion it turns out to be Command + Backspace.

Full listing: http://support.apple.com/kb/HT1343?viewlocale=en_US&locale=en_US

Thank you, I didn't know this shortcut either.