Yesterday, I discovered that the applications should put a special tag in the manifest in order to let the user put them on the SD card.

Today, I tried it on Word Prospector, and
Tadaaa ! It's working great :

(Here in french, obvisouly)

The move is instantaneous, completely transparent.
 And the application looks as fast as when running from the internal memory.
Nice !!

Additionnal note :
I love the Bug-Droid icon when you are connected for debugging !!!