After droves of frazzled customers flooded online forums complaining about their Zunes freezing up, Microsoft confirmed Wednesday that the 30-gigabyte device was, in fact, troubled with hardware issues. http://www.msnbc.msn.com/id/28449091/
Quite a problem for Microsoft, to have a problem with a product line that directly competes with the iPod. That said, I would guess that it's probably the fault of the hardware manufacturer rather than Microsoft itself.
I had a 30GB and it never froze on me, and now I have an 80GB with no complaints. I love 'em, hate ipods by comparison.