Microsoft only acts right when they're losing. It took the loss of dominance on the web to begin to produce a standards-compliant, modern browser. Silverlight never really took off because it had such limited OS support. And, now that they know beyond a shadow of a doubt they can't win the mobile device market (and are even losing some of the laptop market to Chromebooks, and Android hybrid devices), they'll grudgingly open up their developer tools and support other platforms.
I am, of course, happy to see it. But, let's not get too excited about what good Open Source citizens Microsoft have become. Let's let their actions going forward determine that.
Can you expect anything more, really, in the end? It's why we have to always be vigilant against any company taking a stranglehold on any technology. My biggest question in nearly any technology choice these days is "to what extent does this lock me in?". Because the only thing that really keeps these companies working in your favor is the threat that you can, and will, leave if they don't.
I'd say the consumer laptop market is also looking a little scary for them - I think consumers mentally categorize all laptops into two broad groups: "Macbooks", and "garbage". And based on the fact that every major laptop vendor fills out their budget end with embarrassingly bad devices, it's not really an unfair stereotype thanks to the bad reputations these companies have built for themselves.
I am, of course, happy to see it. But, let's not get too excited about what good Open Source citizens Microsoft have become. Let's let their actions going forward determine that.