Understandably, some people are getting pretty excited over the fact that Microsoft has released a fairly substantial body of code under the GNU GPL v2 for potential inclusion in the Linux kernel.
The main point I'd like to underline here is that the reason Microsoft has overcome its historical – and increasingly embarrassing – aversion to the GNU GPL is simply that it is in its own interests to do so: the benefits now outweigh the dis-benefits. That's important, I think, because it gives a hint of what will happen in the future, when Microsoft will release some of its products as open source.
That doesn't mean that Microsoft loves free software or all that it stands for: but it realises that it can use it as a tactical weapon against its rivals – in this case, VMware. Just as importantly, it may be realising that it can help it address some of its most pressing problems: writing complex software, and marketing it as efficiently as possible.
This move also doesn't mean that we should assume the best intentions: there are all kinds of ways – software patents, for example – where things could get unpleasant at a later point. One day, even that might change, as Microsoft understands that opening its software unconditionally is good for everyone, but until then, we should be grateful for small mercies.