Brant,
Have to say this is a market that could be exploited with the right product. I have a speedball that is a good product except for the complete lack of longevity. The function is good but like someone else has said on here, the rotational play is excessive and happens quickly. An issue for me (rightly or wrongly) is also asthetics. The speedball (joplin) are a good looking item, the gravity dropper is one of the ugliest products known to man.
Due to the situtaion of spare parts becoming obselete for my maverick i'll be after another adjustable seatpost, the thing is i don't think any of the current products are any good, or at least proven to be reliable.
I'd certainly be interested with any proucts you come up with?