A Microsoft spokesperson recently talked about the introduction of Google's Chrome browser, and apparently it has them at least somewhat concerned. Microsoft's Scott Hanselman said that Silverlight could face a serious threat from Chrome (and Firefox), if Google and Mozilla continue to improve the execution speed and efficiency of JavaScript. According to him, a "100 to 1,000 fold" increase in JavaScript speed could be expected from the two rival browsers, which would turn it a better choice for numerous web-based applications.
With this in mind, the software giant seems to be considering Chrome and it's fast JavaScript speed to be more of a challenger to Silverlight than Adobe Flash ever was.
This is an interesting change of gears, though it's been clear for sometime now how Google has seen JavaScript fit to build Web 2.0 around with GMail, Google Docs, and many other Google services relying heavily on it.