This is a great idea. You can view it as a clever pyrimid scheme, or an advertising scheme - Kim Dotcom apparently owns the Gem right now, and I am sure he thinks it worth it at that price to advertise Mega in the link, so he would say not a pyramid at all!!
A possible bug though. I don't think the prices reported in the list of previous owners are correct, and the order looks scrambled. Last night vagoods was about to own the gem, and purchase it for 70 odd Bitcoins. Now it seems he got it for 40.41. Hmm, I smell the reek of melting code...
Seriously, I am awed by your bitcoin-foo, I think this a stunningly simple and great idea, and I only wish I had thought of it, I mean really how cool is this? A 1 page business idea that actually delivers, wow!
No vagoods is correct, I purchased right after vagoods for 44 BTC, so vagoods can't have purchased for 70 BTC.
Also I agree that it does have some ad value, after owning the gem for a short period of time, the bitcoingem site sent me over 100 new visitors. I imagine if this bitcoingem site becomes a bitcoin novelty site (like every bitcoin newbie will want to see this site for the lulz), then it can potentially send the last gem owner hundreds of visitors per day, which is worth something in ad value. So it's a win-win situation, you either make some profit, or you get potentially tens of thousands of visitors in ad value.