I am pleased to report that I had only one fewer entry than I expected to receive. Both were perfectly valid, with a unique solution and rotationally symmetric givens. It turns out that with my own "entry" included, all three of us each used only eight givens. I'd imagine six would be impossible, but I certainly haven't proven this. All three puzzles are duplicated below - enjoy (see Puzzle 7 for instructions):
I thought it interesting to note the variances in our compositions. Cameron pulled off what I was aiming for at first and failed to do with only eight givens: no givens on the outer border; Jezendar has a parity apartheid thing going, with the even-celled polyominoes separated from the odd-celled (which e claims e didn't notice until after e built it); my givens are all different values.
With the assistance of random.org, Jezendar has been selected to receive the fifty-dollar prize. Congratulations! You should be getting an email from PayPal shortly.
Shameless plug: there's another way to get a hundred dollars out of me open right now. If that isn't your proverbial cup of tea, fear not - I'm already planning more puzzle contests. - ZM