I thought I remeber reading that one of the new features of iTunes 9 was the ability to put a file right into the iTunes music folder and the file is automatically added to the iTunes library. I can't seem to find this new setting.
The new "feature" sucks, you have to put the items in
~/Music/iTunes/Automatically Add to iTunes/
you can't specify a folder, and you can't put an alias in place of the "Automatically Add to iTunes" folder.
There's no setting; Instead, there's a new folder in your iTunes Music Folder called "Automatically Add to iTunes". Whatever you put into that folder will then automatically be added to iTunes.