Most of the audio engineers I've met--both home and professional--are Mac people, and Avid's ProTools running on a Mac is often cited as the industry standard. But there are Windows loyalists out there.
In late 2007 I took an introductory audio production class taught by David Huber (who wrote one of the bibles on the subject, "Modern Recording Techniques") and Scott Colburn (who has produced albums by The Arcade Fire, Animal Collective, and Sun City Girls, among many others). Both of them used Nuendo from Steinberg (which is basically the upmarket version of Cubase) as their primary digital audio workstation (DAW), and they ran it on a Windows PC.
A Windows XP PC, that is. Both were very diplomatic when discussing software and other gear, but they expressed pretty serious reservations about Vista. Microsoft made a ton of changes in Vista that were supposed to improve performance, including moving certain audio capabilities out of the kernel, but these experts--whose livelihood depends on having a high-performing DAW--thought it was too untested and unknown.
Although they didn't say so, I imagine that the driver incompatibilities reported with other hardware could have been an absolute nightmare with all the gear in a professional recording rig. There were also reports of unstable MIDI timing, drop-outs, latency, and other problems (many of which were addressed by Service Pack 1). They weren't alone: the general advice for audio engineers on Windows was stick with XP. (If anybody had a success story using Vista to build a DAW, I'd love to hear about it in comments.)
In case you haven't heard, Microsoft releases a new version of Windows next week. I've been using the RTM version for a few weeks now and find it far more stable and inviting than Vista was at launch. (Although a colleague did uncover a gnarly power-management problem in Media Center related to a faulty audio driver.) Now, some of the audio experts are starting to weigh in, and it looks like the work Microsoft did to improve performance and compatibility with Windows 7 are paying off in the world of audio production.
Noel Borthwick, the chief technical officer for Cakewalk--which makes a wide variety of audio software for Windows, including the Sonar DAW line--has posted a blog entry describing how the new OS should dramatically reduce latency, particularly on x64 multicore processors. (Borthwick also went into more obsessive detail on Peter Kirn's Create Digital Music blog.) His conclusion: "I will be building a new DAW soon and Windows 7 X64 will be my OS of choice."
The long and short of it? If you're building a new recording system, Windows 7 sounds like a more reasonable choice than Vista. But if you've got a system that's already working well, don't mess with it--there still might be driver incompatibilities with older gear, and upgrades from Windows XP require a clean install, meaning your old settings will be lost and you'll have to reinstall your apps.
Correction, 2:34 PDT: This post incorrectly characterized the audio-related changes that Microsoft made in Windows Vista. Microsoft moved certain audio functions out of the kernel and into the user stack.