Some are even saying that this is a phony little war that doesn't hurt anyone. Since the just announced OS is vaporware at this point and mostly targeting for netbooks in the near future, Microsoft's immediate revenue is not in any danger. However, you can count on Microsoft throwing counterpunches to nullify low-end threat the Chrome OS poses.
Even with mobile phones, Microsoft gained marketshare in 2008/2009 and even outsold iPhone believe it or not. Android phones are just starting to come out, so we will have to see how big they are going to be. As for the netbooks, it is reported very recently that Windows XP ships in 96% of netbooks sold worldwide, up 10% from a year ago. Linux originally had good momentum, but it is losing steam due to a combination of users preferring familiarity of Windows and Microsoft's deft use of pricing and its size. It just shows how Microsoft fights back.
Also, note that Google says first netbook with Chrome OS is not out until 2010H2 and Windows 7 (which is expected to be netbook friendly) is due out in a few months. Microsoft would have the netbook market for 1 full year. I think all this adds up to moves and countermoves [at least for now].
Otherwise, Chrome OS better be one sweet friggin doozy.