> What difficulties do you (or anyone, for that matter) have with Rails
> that you think a book is needed?
> 
> Do people find it that complex?

IMHO, Getting a basic rails app up and running is not diffiicult...
just look at Curt's wonderful tutorial on Onlamp
(http://www.onlamp.com/pub/a/onlamp/2005/01/20/rails.html).  But there
seem to be a lot of nuiances and tricks that can be used that are not
immediately apparent to a new rails user.

A book could address a lot of issues, such as advanced configuration
(such as webrick vs. apache, mod_ruby vs fastcgi, etc.), debugging
(such as with using breakpoints), an in depth description of how Rails
handles sessions (so one can use it properly with the right amount of
security), proper deployment of rails (for example, what's the best
way to deploy multiple Rails apps on a single account?), unit testing
on a web framework... I would personally find a Rails book extremely
useful.