I just got my first critical capture ever! And on a rare Pokemon too! YES! ^^
It happened with a Throh I ran into while training my Oshawott in Black that I got in a trade. I'd run out of Great Balls and Ultra Balls trying to get the damn thing, and once I chucked a Timer Ball, one of my favorites, actually, critical capture! Woo! Throh is rare in Black because it's only found in shaking bushes in the route between Nacrene City and Pinwheel Forest.