I copied this from the Disney website:
Q: I am a Passholder (or have a valid Multi-Day Ticket or a Seasonal Pass that I will use for admission on my birthday in 2009), so I don’t need to take advantage of this offer. If I register, is there anything else I could receive on my birthday?
A: Yes, you have several options which are available for you to select once you arrive at the Park with your confirmation message and your proper ID. You can receive:
* A special birthday FASTPASS® badge+ for certain attractions at the Theme Park you visit on your birthday; or
* A 1-day Magic Your Way base ticket for you to use any time until your next birthday; or
* A birthday fun card in an amount equal to the price of a 1-day Magic Your Way base ticket* for you to use on your birthday for merchandise, recreation or fun activities at select participating locations at Walt Disney World® Resort.