A couple of weeks ago there was quite a bit of discussion about adding unit testing support to all versions of Visual Studio 2005. OK, so I'm late to this party, but here's my 2 cents.
I think Jamie Cansdale nailed it when he said the unit testing should be part of the BCL, not just Visual Studio. If you buy in to test driven development (as I do), then unit testing is a core part of your development process. With the .NET framework SDK, Microsoft has touted the ability to write .NET code without an expensive IDE (call it Notepad Driven Development if you must - plays on TDD seem to be all the rage right now). If unit testing is a core part of that development, wouldn't it be natural to put a simple unit testing framework in the BCL and the .NET SDK? After all, according to TDD'ers, there can be no development without unit tests. Include a simple (even console mode) unit test runner in the SDK, and NDD/TDD lives.
The response to all of this from Microsoft seems to be a combination of “the benefits of Team System is the integration and reporting” and “hey, we need to make money selling products here”. The way I see it, including unit tesing in the BCL and Visual Studio would actually help sell Team System. Why? Because the more people are unit testing, the more value Team System adds. People won't buy Team System to get unit testing - they don't need to. But once they have their test suites, Team System, with its checkin policies, change management, reporting, etc adds even more incremental value. In other words, include unit testing in VS2005 to up-sell developers to Team System.