I've been using .NET since it's beginning. It's an excellent platform which I think is hard to beat. When it comes to tools Microsoft are unquestionably the best. Other companies just cannot compete. Their stuff just WORKS. I've only recently moved on to using WPF and also Silverlight for Windows Phone 7. Again the platform and tools are just too good.
I don't think (hope) they will abandon .NET so easily, as mentioned this is just one of their cool new features they have added to their arsenal which they are unleasshing to the public. If we consider the recent developments around the Windows phone platform and Silverlight. Surely they are forward thinking and wouldn't base their new mobile platform on a tech they themselves are going to make redundant. A platform Microsoft are really pushing hard.
MS have invested a lot of time and effort into building the powerful .NET platform and toolset which developers all over have come to love. As ever I'm sure they're keeping some things close to their chest. I guess if worst comes to worst then Microsoft will probably provide us with the most useful tools to aid developers in their next journey. Well there's my thoughts on paper. Still annoyed. Come on Microsoft, help put us all at rest.
P.S. If anyone is considering Windows Phone 7 as a platform or even a personal device try it out. You won't believe how good it is until you try it. This coming from an ex Android fanboy