In the day and age of the online world I can't see how it'd be particularly useful, though there are obviously situations where people don't have internet access, so it isn't completely outdated to have an offline help file.
It's a lot of work, however, and as stainsor pointed out it'd be out of date alot, whereas a wiki is very easily editable and maintained by several people.
Probably after 1.0 we'll put together a collection of references and information, when most things are set in stone.