Microsoft: (Our) Virtualization isn't mature
I agree with Microsoft, somewhat. Their VirtualPC offering isn't mature enough for broad consumer adoption, indeed I'd go as far as saying it just isn't mature regardless of where you choose to use it.
VMware on the other hand, now I've been using that since it was in beta, long before EMC spotted that it was a goldmine and snapped it up. More and more people come to the free player and server products every day, good for them.
Of course while it's easy to think that this is a slap against VMware or to a lesser extent Xen ('cause you know consumers are lining up to try and get Xen running on their systems), the cold reality is that Microsoft are finding it increasingly difficult to grow their consumer OS business. It's ubiquitous so with Vista's multi-tiered offerings what you're really paying for is go faster stripes, alloy wheels, a Corinthian leather interior and a rear spoiler.
If gamers are to be beleived you're also paying for a 10% performance reduction over running the same game in WindowsXP, so unlike the MacOS X reference builds I won't be running out to spend my money on Vista anytime soon.