Back in the days of Unix, you couldn't even close a software without reading the man page first. Then came Mac and Windows with consistent menu layout and keyboard shortcuts, but you still saw paper user manuals shipped in the shrinkwrap box, which described each and every single operation possible in the app. After the Internet, help files became html documents.
Nowadays with Web 2.0 applications, you hardly see the Help. Even if it's there, they simply describe some specific tasks. In other words, the apps are relying more on the common sense or don't-make-me-think factor of the user base.
Years ago Microsoft came up with a concept called Inductive User Interface, which basically tells programmers to put in instructions on the apps itself, but I am not sure how popular that idea is.
Are help files, user manuals, and context sensitive online help with F1 key dead? Have I failed if user could not find out what to do from the UI? If not, what degree of help should I provide? (both for desktop and web app)
EDIT: How does documentation/help file mesh with agile development methods? For example, should the developers think twice before UI changes that may obsolete a bunch of screenshots?