Depending on which media outlet you believe, Vista is either doing poorly or doing so well that it's hurting OS X sales:
MacNN | Vista awareness doing little for sales:
"Vista promised better performance, reliability, security, and a revolutionary user interface - but it appears consumers looking to upgrade are not ready to buy into the promise," said Harris VP Milton Ellis.
Macworld: News: Vista taking a nibble out of Apple in OS wars?:
Windows Vista more than doubled its market share in March from the prior month, while the share of computers running Mac OS X fell for the first time in nine months, according to statistics released Thursday by market research firm Net Applications. [original source: Computerworld]
I think that CW is primarily a PC-related outlet, so maybe they have an axe to grind against Apple. No matter what, MS is still following Apple's lead in every way. So for a company that's falling further behind MS, Apple sure is dictating how the market goes:
Microsoft changes tune on selling DRM-free songs - Yahoo! News:
Following digital music pioneer Apple's lead yet again, Microsoft said this week it will soon sell digital music online without DRM (digital rights management) protection.