No I haven't yet, just comparing a DVD I have that would flicker madly under XP because it would only be Bob'ed, but under Vista it's being deinterlaced but isn't flickering madly, so I assume it's using something better than bob, either way it's good enough for me, just might not be VA, I should check it I guess :P
If I turn AERO on then the DVD flickers madly again because of it being only Bob'ed.
EDIT: I just ran the PAL DVD test, there isn't any obvious parts of the DVD to show if VA is working, I just had to look at the TV and compare it to the screen shots on my laptop. From what I can tell though it does look as good as the VA screen caps.
I'm pretty happy with this, I nearly went out and bought a new video card so I'd get VA for my interlaced PAL dvds. Now I don't have to