Joelonsoftware takes issue with the .NET strategy. He's annoyed about the lack of an upgrade path (in his case from VB) and he basically thinks Microsoft is squandering their platform advantage by moving to new things all the time. There's no lock-in in new things.
I don't really buy it. It's not like the Windows API is going away, it's just that you can consider it frozen. If and when the new way (.NET) proves as productive as hoped that will finance the upgrade in and of itself. As far as I'm concerned the new stuff in .NET is mainly about increasing developer productivity and very little about enhancing user experience.
Obviously, if MS fails to deliver the gains in productivity they will have made a terrible strategic blunder.
Among the interesting stuff in this worthwhile essay is an assertion (borne out by the leaked windows source code) that it is simply not true that Microsoft has deliberately broken thid party products to make room for their own. In contrast, a lot of effort has gone into keeping features around to ensure smooth upgrades.

[UPDATE: Loosely Coupled chimes in and agrees. Phil Wainwright summarizes his position in the title of a post: Avalon: Microsoft's microchannel, i.e. an attempt to redefine the PC industry that will fail (like IBM's microchannel arcitecture) because everyone is locked in to todays Windows. In an earlier post he has coupled this with the notion that XML is to Microsoft as PC was to IBM, meaning that the embrace of open standards of information interchange automatically opens up the platform. It will either stay open and compatible or become irrelevant. To carry the analogies one step too far: If Microsoft is IBM in this story then the network is Microsoft. Staying open and network compatible is more important (and cost efficient) than staying Microsoft compatible today - just as staying Microsoft compatible was better back when IBM introduced the PS/2-OS/2 combo]

The power of both arguments depend on whether or not Microsoft does in fact hold monopoly power. It will take that kind of power to keep customers locked in to Windows (and not switch them to Linux or at least Open Office).