Grumble Grumble Grumble
Microsoft has already posted a solution to this problem...
Evidently, the issue isn't limited to the Flash ROM update, but is common to all 30GB Zune models (something to do with not handling leap years correctly!!!)"We expect the internal clock on the Zune 30GB devices will automatically reset tomorrow (noon, GMT)," Microsoft said. "By tomorrow you should allow the battery to fully run out of power before the unit can restart successfully, then simply ensure that your device is recharged, then turn it back on. If you're a Zune Pass subscriber, you may need to sync your device with your PC to refresh the rights to the subscription content you have downloaded to your device."
Users report 30GB Zunes seizing up; Microsoft IDs clock bug | Microsoft - CNET News