Note: This is a ponzi, that's why it's in the gambling section. It's risky.EDIT: Check out Bitcoin Gold - get in early while you can, and if you get in late you can get the script behind it for free!Bitcoin gem takes the concept where you buy the gem for XX bitcoins (currently 78.76 btc). Then, the price of the gem will be raised to 86.64 btc, and you get 82.7 btc sent back.
http://www.bitcoingem.com/index.phpThe higher the price is, the less likely people is going to buy in. The price is raised by 10% each round, and the higher the price is raised, the more profit there is (but it will collapse/halt in less rounds). It might be interesting to allow users to buy "shares" of the gem and pull together fractions of the price, so future rounds would require (i) more users and/or (ii) higher amounts.
There's also the free advertising aspect, which might be worth it for smaller amounts and advertising bitcoin-related services (eg a new gambling game, etc).
Also, the system requires 6 confirmations, which delays the time when a new round happens. Looking at the list of transactions, it seems that at this price point there are a lot of people that purchase quite soon after 6 confs.