Jonathan and Lisa Price have a nice article on writing FAQ and covered many points that we may not think about. For instance, if you have a large site — you might want to show the FAQ or Help that’s relevant to the page users are on rather than give them the whole thing to dig through. Many software applications do this — give you the Help based on the window you’re viewing.
I believe FAQ are best served when all of the questions and answers appear in one page — unless it’s ridiculously long and neds breaking up. The reason for this is because some users will use their own browser’s search instead of a site’s search — they want to find a keyword on the current page instead of browse the whole site.
Add items to the FAQ as you get e-mails from users, see questions popping up in the forums or on the Internet — don’t assume people will find their way to the other sites that answer the questions… do people a favor by offering everything in one place. Users appreciate it and it never hurts to go the extra mile… actually, they expect you to have complete answers. Hey, it saves you time as people won’t contact you if they can find the answers on their own. Of course, not everyone thinks to check the FAQ — but every bit helps.
Notice I never used the “s” in FAQ as in FAQs? Skipping it was hard, but I learned to just write “FAQ” because “Q” means “questions.” Why write an FAQ if you only list one question?