I've always liked the Laprade seatposts, both for function an looks. As for the flutes, I'd guess they're to add stiffness. There was a recent thread here with pics of a Colnago Conic SLX bike, and the tubing on the downtube was "ribbed" for stiffness. The flutes on the Laprade posts look like they'd serve the same purpose. But yeah, you have to make sure there's a good bit of grease in the seat tube to seal the gaps caused by the flutes-