Mafia Wars has rolled out a new loyalty program, and it has three levels Emerald, Gold and Platinum. Each level can earn various rewards, including Loyalty Points (which can then be used to buy items exclusive to your level). Essentially, the goal of this whole program is to encourage you to spend more money on the game -- if you do -- you'll get exclusive access to rare items, beta programs and Mafia Wars events (among other things).
Seems like most everyone stars out at Emerald and will work their way up by spending more money. Emerald level players get the following benefits:
Earn 1 x Loyalty Points for every dollar you spend
Use these points to buy Emerald items
Get access to special discounts on reward points.