There have been a lot of reports on twitter and other sites of users with 30Gb Zune music players failing en-masse as the clocks ticked over to New Years Eve (31st December, 2008).
Microsoft has acknowledged there is a problem and that they are working on a solution. Interestingly enough, it seems to only affect players with a 3.x firmware.
Source: http://arstechnica.com/news.ars/post/20081231-30gb-zunes-prepare-for-new-year-by-locking-up.html