Do I need permission to include Web site screen shots in my ebook?

In which a reader asks about the legal requirements for obtaining written letters of permission prior to including screen shots from different Web sites (or applications, for that matter) in an electronically published book.The answer is, as is typical with the law, "that depends", and while most companies are cool with any sort of publicity, some large firms really try to control the message and throttle the messenger to a rather amazing degree:

    Are approvals needed for web site screen shots?

Disclaimer: I'm not a lawyer nor am I an expert on the law. I have published almost two dozen books, however, and worked with a number of different publishers, so my view is at least reasonably informed.