Dear Rich: I have a question. I'll be using a lot of screenshots from different websites in my book. Do I need to get permission for that or is it a fair use? I'm so glad you asked. Conventional wisdom (and the Electronic Frontier Foundation) says that an unauthorized screenshot is an infringement. That said, the use of screenshots rarely triggers a complaint because either: (1) the copyright owners don't want to complain about something that promotes their company -- for example, an online tutorial about using Microsoft Word, or a book about starting an eBay business, or (2) the copyright owners believe the use is likely to be excused as a fair use. Although issues don't often arise, occasionally copyright owners do complain -- for example, Apple complained about pre-release screenshots of the iPhone. Some sites place limits on your use of screenshots in their user agreements.
Keep in mind that if the copyright owners do complain, the results can be unfortunate--it may disrupt publication of a book or other product. Perhaps a more important issue to consider is whether what you are doing is likely to anger or annoy the copyright owner. If it is, proceed with caution and review your use of the company's trademarks so that your use doesn't imply an association or endorsement.
P.S. In the future, sites will be able to block screenshots.