Apple's yearly developer conference should see iOS 8, OS X 10.10, and likely some hardware.
Apple Slowly Ramping Up iPhone Developer Program
In the email, Apple thanks the applicant for their interest in the iPhone Developer Program, and states that the iPhone Developer Program is only available to a limited number of developers during the beta period. Apple plans on expanding the program during the beta period and will contact applicants again "at the appropriate time".
Despite theories that every applicant has received the same letter, we can confirm that some developers have already been accepted into the iPhone Developer Program.
The $99/year iPhone Developer Program should not be confused with the SDK itself, which is available for free download. iPhone Developer Program provides a developer with the beta release of the iPhone 2.0 Firmware as well as a developer certificate which provides the ability to install applications onto the iPhone itself. Without the certificate, developers are only allowed to install applications onto the iPhone Simulator that accompanies the free SDK.
It is believed that the iPhone Developer Program will be open to all comers after June when the program is out of beta. At that time the iPhone 2.0 firmware will be publicly available.