OK, you are forgeting one thing, Google is a for profit corperation, their mission is not to "kill Microsoft," thier goal to maximize profit, Microsoft has the exact same goal. Google and Microsoft just happen to be in a Oligopoly right now which is why they both are focused on each other, because any move by one of them (be it hostile to the other company or not) will affect the other. I'm sorry but Microsoft and Google both realize that users will not bear to have required advertising built in to the OS. Which is why I fail to see is where Google plans to make its profits by working on ReactOS; in order for investment in ReactOS to be profitable, it must hold potential to increase Google's revenue. One possible source of revenue is if Google plans to make a GoogleOS, base it on ReactOS, and sell the OS. Of course they say they have no plans to do so at this time, noone really knows if they are planning to or not (expect of course their upper managers.) But don't just assume that Google will automatically invest in the project just because it could hurt thier competitor's sales, they are interested in thier revenue, not Microsoft's.
David Hinz wrote:
When you look at what MS wants to do (advertisments on every pc...) this perfectly fits, because then google would provide the ads (if we would really want to do this, but I don't think so) and not MS.
Google and MS are the biggest enemies in this market, so Google is happy over every cent MS doesn't get. If Google gets this cent or not isn't that important for them in that moment, the most important thing for them is that MS doesn't get it. And the easiest way to reach this goal is to "steal" MS the platform they need, Windows. If they use Linux, ReactOS or whatever doesn't interest them. You can see this when you look at the relationship between Google and Sun, they said, that they want to work together, I think the background is, that Google wants as many users as possible not to use MS Office, because MS wants to use it as an advertisment platform.
I hope you see, why such a relationship would be of interest for Google.