Comex has promised the iOS community with iOS 4.2.1 untethered jailbreak to launch before the Christmas but
this tweet from Comex means that nothing is going to be released by the Christmas, i.e. we may not see that untethered jailbreak for iOS 4.2.1 by this Christmas. Though keep the hopes up!
Yeah, don't forget that the iPhone Dev Team already has the backup plan and may be merged with Redsn0w to bring 1-click untethered jailbreak for iOS 4.2.1. Comex's userland-jailbreak may take longer. Anyway, stay tuned for more updates as they come !