Huh. What happens if you drag-and-drop a bitcoin URI link onto the Bitcoin-Qt window?
That works, but it is a bit of a PITA. Also, you have to drop it in the big blank area, it won't work if you drop it anywhere else such as in the address field.
Aha! So I'm not just hallucinating the whole bitcoin URI support thing. Why doesn't it work the proper way, I wonder?