In developing good incentives to get prospects to sign up for an email newsletter or any kind of free club membership, the issue of 'fair exchange' is often overlooked. The incentive you're offering and the commitment they're making need to have approximately the same value.
"Tell me your birthday, and I'll give you a birthday treat" isn't just fun, it's also sensible and fair. What can you do to make your incentives sensible, fair and fun?
MarketingSherpa: How to Grow an Email List From Nothing to 2 Million Loyal Fans in 2 Years, 2008-Jun-11(subscription required)
It seems that everyone likes free ice cream on their birthdays. All of the steps taken to make the birthday club emails attractive, functional and abuse-free produced an outstanding response. Almost 2 million birthday club members have signed up -- already 400,000 more than their regular subscriber list. This translates into 45% of recipients downloading and printing the coupons.