The iPhone Dev Team has just released the second beta of Redsn0w 0.9.7 to convert tethered jailbreak of iOS 4.2.1 to untethered on new-generation iOS devices. The second beta is still for testing only so stay away if you rely on your device or care for an unlock.
Redsn0w 0.9.7b2 fixes all the native app crashes (including Task switcher). This is the only change from the first beta that was released earlier today. Just follow the guide posted here to achieve the untethered jailbreak for iOS 4.2.1. In case you got any problems usbmuxd in beta 1, this won't help, it's better to wait for another beta.
Download Redsn0w 0.9.7b3 for Mac OS X