Apple released iPhone OS 4 beta 2 along with iPhone SDK4 beta 2, registered developers can download via their developer account developer.apple.com. If you are upgrading from beta 1 to beta 2 you must turn off the passcode before upgrading. If you back up your device on a computer running Mac OS X, you must install the Beta 2 SDK on that computer before you attempt to backup and restore the device, otherwise the device will refuse to proceed with the backup. If you also reinstall iTunes, you must install the Beta 2 SDK after installing iTunes.
Beta 2 comes with lots of major changes including multitasking time, the time for task completion has been changed from 5 to 10 minutes.
Stay tuned for more.