Delta just rolled out their April birthday promotion:
YOUR BIRTHDAY GIFTS MAKE IT POSSIBLE.
It’s time to start the celebration!
Our birthday gifts to you are waiting: You can get 2,000 bonus miles on your next round-trip flight and a $100 e-certificate toward a Delta Vacations® getaway.
First register, then book your round-trip ticket by April 30, 2011 and complete your travel by May 31, 2011 to receive your 2,000 birthday bonus miles.
My birthday was in March and I had flights already booked and I still received the bonus miles. So it seems like as long as you register and then fly on a paid ticket during the period, you should get the miles.
And if you aren’t eligible for this offer, make sure your birthday is in your delta.com profile
Delta.com -> Skymiles -> Manage my account -> Manage my profile