My 30G locked up on the boot screen... Synced it and fully charged yesterday.
Strangely enough, I also have a Toshiba Gigabeat (windows mobile, very similar to zune) that has also locked up in the menu.
Two of my kids also have Zunes, but they aren't awake yet. I'm going to have them not power up until we hear more.
It's -8 here in Minnesota, but the Zunes seem more frozen