Yesterday's headlines were all about Microsoft's release of the Hyper-V virtualization software, so it's inevitable that today we see the rush of reviews.

And on the whole, they're not bad. Even those who point out the system's flaws are quick to note that its positive attributes more than make up for the negatives, giving Hyper-V a good shot at drawing significant numbers of users away from VMware.

Author and consultant Jonathan Hassell notes that the most significant difference between the beta releases and this week's RTM (release to manufacturing) version is speed. Running the system through a QLogic Fibre Channel HBA yielded performance results that were about 97 percent of physical hardware when running high I/O applications like those churned out by mail and database servers. The performance is so good that Microsoft has been running its own msdn and technet sites on Hyper-V for several months now, and no one has noticed the difference.

Customers using earlier versions of Microsoft virtualization technology are also reporting a performance boost, according to this report on CIO.com. Security firm Kroll Factual Data was running about 300,000 transactions per day on about 1,600 instances of Virtual Server. Adding only about 100 Hyper-V machines has already bumped performance some 20 percent.

One of the major drawbacks, though, is the lack of live migration, says InformationWeek's Joe Herrick. VMware, Citrix and even Sun's Xen system all have it, so it will be interesting to see how long Microsoft can maintain that its customers will be satisfied with near-real-time migration.

Hyper-V also doesn't have the kind of management capabilities promised in the Microsoft System Center portfolio, nor can you run it outside of Server '08, but none of that should detract from what it does provide, according to Mitchell Ashley, CEO of systems integrator Converging Network. Delivering a solid hypervisor ahead of schedule lays the foundation for a full-featured system later. Adding all those features now would have made the system clunky, expensive and bug-ridden.

A lot of the commentary of the past few days has labeled Hyper-V as the VMware killer. That's probably overstating things a bit. Microsoft is very powerful and has a lot of leverage to wield, but the people at VMware aren't fools. They're perfectly capable of sizing up the competition, and then adapting to it.