Haha, I'm surprised this rumor is still floating around. Nonetheless, I've experimented with birth control pills and cultivation.
I've only tried BC pills with one grow (my first, in fact), so the results are anything but conclusive. Using a handful of freshly purchased Nirvana seeds, I ended up with only 1 male and about 6 females. I applied the pills by dissolving one first in water, then including this elixir during regular waterings (this was a soil grow).
With all that being said, I dont believe the pills had any affects on the plants. Birth control pills are comprised of synthetic hormones, estrogen being one of the most abundant. I can't image plants absorbing these hormones; even if they did, they won't have the cells or processes to utilize human hormones. Who knows, maybe the pills have something else