No I haven't. Looks interesting, but by the time you bounce the low power built-in flash up and off the ceiling, you won't likely add much illumination to the scene, especially over any distance at all.
Stop by the Audio Note room and I'll lend you my SB600.
Dave
I don't know. In manual mode you can crank the built in up pretty nice. Not a substitute for an SB or anything, but it puts out quite a bit of light. I'm still learning to use the D40 indoors. I just don't take many photos inside at all.