And, about motivations, I will not trust Microsoft. They are constantly threatening Linux users with patent suits and forcing them to license undisclosed technologies, maintaining an atmosphere of legal uncertainty. Why would anyone want to use tools that are vulnerable to such attacks?
Given all that background, it makes sense for people to be cautious -- though not unremittingly and unthinkingly hostile -- regarding Microsoft.
Now, for me, if I was developing on the CLR, I would very much consider using IronPython. Though having said that, I wouldn't consider developing for the CLR, because it isn't open source and doesn't run on Linux. Instead I might use the JVM, which seems to be acquiring a good ecosystem of languages (Groovy, Clojure) and tools (ANTLR, various IDEs) that run on it.
Instead MS though their dominance of the PC space meant they could relax and didn't need to develop good products. And now Apple is eating their lunch.
I find it very sad that very nice tools like IronPython, IronRuby and the whole CLR stack have such threats associated with them. I would love to use them, but I find it risky and I do not enter any course of action that may empower Microsoft against the FLOSS community.