Microsoft's stance on open source is pretty clear to me:
Microsoft has no plans on flipping any of its flagship products to open source. Period. The effort vs. reward equation just does not make sense since it would be a HUGE effort to make the code consumable by a community.
Microsoft sees some value in understanding open source; hence its investments in Port25 and CodePlex.
Microsoft sees some value in open source technologies that run on or interoperate with its platforms and products.
Microsoft will aggressively fight/compete with products (open source or closed source) that pose a threat to its core products. Hence, Bill's points re: Red Hat Enterprise Linux.
Now, while I do work at Red Hat, I should also disclose that I know and respect Bill Hilf. We started working together a few years ago on the JBoss / Microsoft alliance. At that time, we agreed to set aside the Java vs. .Nyet(sorry Bill) debate and focus on better serving our developer and production users that target Windows. Among other things, we focused on interoperability (Web Services, etc.) and have participated in various plug-fest workshops over the years.
So, I have to admit that I'm disappointed to see Bill Hilf dance around the questions and hide behind such FUD as proprietary software "guarantees".
As much as I hate to say it, Microsoft could learn something from IBM's strategy. They make no bones about it: they work in the open source on piece-part components that they Bluewash into their closed-source products. While it's not a pure open source business model...it's clearly an open source strategy.
C'mon Bill, drop the FUD (that's Ballmer's shtick, not yours) and just say it as plainly as I have above.