"It's a pretty impressive release," said Van Baker, research vice president at technology research firm Gartner. "It further extends [Apple's] lead in terms of the kind of things the platform can do."

The event, held on the company's campus in Cupertino, Calif., focused on features for both and . Of particular note was a long-promised feature that has yet to see the light of day--.

Push notification lets applications that aren't open receive notifications when something has changed. For instance, an instant messaging (IM) client could alert you when someone sends you new message, without having the application open.

"Apple just gave developers another good set of reasons to get on the platform," said Michael Gartenberg, vice president of strategy and analysis for media and technology research firm Interpret. "Apple is making sure that the only platform you are going to get this type of functionality on is the iPhone."

Another area of great interest to developers was in-app purchases--the ability to sell products from within an app itself. Apple gave the examples of being able sell additional levels for a game or to sell e-books books, all without making customers take a special trip to the App Store.