You can use Apple's developer tools with the PhoneGap library to make a single app that runs on iPad and all the phones, including BlackBerry. In the near future, PhoneGap will support PlayBook, because PlayBook also has WebKit, it is essentially Apple-compatible. So anyone that is put off by RIM's developer tools can work with Xcode/PhoneGap to build one app right now for all currently existing platforms and when PhoneGap adds PlayBook you will be on there immediately. This is not necessarily a solution for everyone, but is ideal for some developers. It is also more cross-platform and more open than AIR.
PhoneGap
http://www.phonegap.com/
Apple Developer
http://developer.apple.com/
Good luck to RIM. PlayBook is about a thousand times more interesting than Motorola XOOM. I'm looking forward to deploying my apps on PlayBook if the device happens as planned.
This was a comment posted by a developer on blackberry developers blog...by John Doey...makes a lot of sense
Posted from my CrackBerry at wapforums.crackberry.com