Microsoft has received much undeserved press about their recent release of Linux drivers for their virtualization technology under GPLv2. I say “undeserved” because I don't particularly see why Microsoft should be lauded merely for doing something that is in their own interest that they've done before.
Most people have forgotten that Microsoft once had a GPL-based product available for Windows NT. It was called Windows Services for UNIX, and AFAICT, remains available today (although perhaps they've transitioned in recent years to no longer include GPL'd software).
This product was acquired by Microsoft when they purchased Softway Systems. The product was based on GCC, and included a variety of GNU system utilities ported to Windows. Microsoft was a compliant distributor of this software for years, right during the time when they were calling the GPL an unAmerican cancerous virus that eats up software like PacMan. The GPL is not a new license to Microsoft; they only pretend that it is to give bad press to the GPL or to give good press to themselves.
Another thing that's not new to Microsoft is that they have no interesting in contributing to Free Software unless it makes their proprietary software more desirable. In my old example above, they hoped to entice developers who preferred a Unix development environment to switch to Windows NT. In the recent Linux driver release, they seek to convince developers to switch from Xen and KVM to their proprietary virtualization technology.
In fact, the only difference in this particular release is that, unlike in the case of Softway's software, Microsoft was apparently (according to Steve Hemminger) out of compliance briefly. According to Steve, Microsoft distributed binaries linked to various GPL parts.
Meanwhile, Sam Ramji claimed that Microsoft were already planning to release the software before Hemminger and Greg K-H contacted them. I do believe Sam when he says that there was already talk inside Microsoft about releasing the source underway before the Linux developers began their enforcement effort. However, that internal Microsoft talk doesn't mean that there wasn't a problem. As soon as one distributes the binaries of a GPL'd work, one must provide the source (or an offer therefor) alongside those binaries. Thus, if Microsoft released binaries and delayed in releasing source, there was a GPL violation.
Like all GPL violations (and potential GPL violations), it's left to the copyright holders of the software to engage in enforcement. I think it's great that, according to Steve and related press coverage, the Linux developers used the most common enforcement strategy in the GPL community — quietly contact the company, inform them of their obligations, and help them in a friendly way into compliance. That process almost always works, and the fact that Microsoft came into compliance shows the value of our community's standard enforcement practice.
Still, there is a more important item of note from a perspective of software freedom. This Linux driver — whether it is released properly under the GPL or kept proprietary in violation of the GPL — is designed to convince users to give up Free virtualization platforms like Xen and KVM and use Microsoft's virtualization technology instead. From that perspective, it matters little that it was released as Free Software: people should avoid the software and use platforms for virtualization that respect their freedom.
Someday, perhaps, Microsoft will take a proper place among other large companies that actually contribute code that improves the general infrastructure of Free Software. Many companies give generally useful improvements back to Linux, GCC, and various other parts of the GNU/Linux system. Microsoft has never done this: they only contribute code when it improves Free Software interoperability with their proprietary technology. The day that Microsoft actually changes its attitude toward Free Software did not occur last week. Microsoft's old strategy stays the same: try to kill Free Software with patents, and in the meantime, convince as many Free Software users as possible to begin relying on Microsoft proprietary technology.