As much as I love the iPod and despise the Zune (no podcast support and the DRM issues in particular), I regret to admit I feel the Zune will hold at least 50% of the market within a few years.
(EDIT: OK, maybe 50% is overstating it. I actually don't think any company will have 50% of the portable music player market in a few years -- not even apple. I'm just saying I don't think the Zune will be a failure)
Just because it sucks, doesn't mean it won't win the war, Microsoft have been proving that for decades.