Are you annoyed each time you change a file extension (like from .avi to .mpg) when you have to click on "add" to approve the new extension?
Simply hit escape, which normaly defaults to "cancel", but in our case corresponds to "add", and voila! I guess this hint works for all kinds of dialogs setup like ok-cancel templates.
[Editor's note: I"m not sure if this is a bug or a feature, but it definitely works as described and saves a trip to the mouse. I could not, however, get it to work in other Finder dialogs.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=2002022209280419