The Export sheet has two buttons, Cancel and Export. Cancel is already keyboard-enabled (or acts as if it is); hitting ESC closes the sheet. But Export cannot be activated with the Keyboard; one must use the mouse.
If Export were the default button, hitting Return or Enter would "press" it.
(I'm using AD to build multilayer graphics; I typically have ten or so exports per graphic with different layers turned on and off. I've assigned Command+E to File > Export..., so once I've set the format and directory for my first export, I can do everything quickly through the keyboard, except for "pressing Export" in the Export sheet. Moving the mouse between the Layers palette and the Export slows down the process quite a bit.)
