I think Microsoft's biggest mistake was waiting way too long to bundle the .NET framework with Windows. They waited until Vista to do this, and since Vista was

I think Microsoft's biggest mistake was waiting way too long to bundle the .NET framework with Windows. They waited until Vista to do this, and since Vista was so poorly received, even now you can't be 100% sure. Making things worse is that if you do run a .NET app without the framework, you get a cryptic error message that offers no help whatsoever. This poor out-of-the-box behavior made a lot of people wait to develop .NET apps, IMO. Lion's "you need to download Java to run this, would you like me to do that for you?" method is way better. But, 20/20 hindsight. Other than that, it's a fantastic platform and I love developing in it. I don't think it's going anywhere.