I promised to let you know how the purple cauliflower was. I prepared this purple prize by steaming it just until done, and then mixing a bit of butter (yes, butter, not margarine--butter is healthier) in with it.
It tasted like...cauliflower! It had a slightly bitter aftertaste, which cauliflower also can have, but the bitterness seemed just a bit stronger than its white cousin's. The cauliflower-ness was a bit milder. All in all, I wasn't displeased; next time, however, I might mix in just a pinch of sugar to offset the slight bitterness.
I would definitely buy purple cauliflower again (although perhaps not frequently), simply because the taste is close enough to pass for cauliflower and the obvious abundance of anthocyanins make this a healthy veggie choice. I also hear, however, that somewhere out there, orange cauliflower exists, which would be high in beta carotene. I hope to see some appear at the farmer's market so I can give that a try!