Jason Matusow, Microsoft's director of open source licensing, has started blogging. His first post wasn't more than the classic "Hello World" thing. So, his second post on the subject, More Open Than Open, is his first substantive post.
He certainly comes out swinging. This is a first-rate rundown on variations in open source licenses, and how some are more "open" than others.
With the number of Microsoft bloggers aggregated through MSDN Blogs, I'd suggest subscribing to Jason's blog directly. You aren't going to want to miss any of his articles.