Reportedly it's a firmware issue with Samsung, more accurately those with firmware versions JI9 and JJ4 are experiencing problems, while the JK1 firmware, according to ZDnet, are doing okay. While we have no way to confirm that 100%, it seems best for those users to avoid the update. In fact, that may be easier than it looks since from our perspective (here in the States) Microsoft has either yet to or has indeed put a halt to rolling out the update (both my Quantum and HD7 have yet to be flagged for an update, even when force-checked in Zune desktop).
Microsoft is evidently set to push out a "fix" update within three days time, noting in their support forum:
We would recommend at this time, not to retry the update, as subsequent attempts will fail similarly. While we continue to investigate the issue, we would ask that you not attempt the update until your device alerts you of another update opportunity, in approximately 3 days time.
Microsoft offers some advice if your phone gets stuck during the update process, including disconnect the device, pull the battery and put back in to reboot. For those who have a "bricked" device i.e. it won't boot at all and cannot be hard-reset, you are advised to contact your carrier--reportedly AT&T is being cooperative in this regard and covering the phone under warranty.
