Comex has tweeted saying that he may not be able to complete his untethering of the current jailbreak by Christmas.
I think I'm going to miss my Christmas deadline...
On Tuesday the iPhone Dev-Team announced that their 'backup plan' untethered jailbreak is nearly ready and will not require a restore of your device.
Comex's untether is more extensible and should not require access to the developer only 4.2b3 IPSW; thus, it's suggested that users wait for his.