I wrote an Upgrade to Rails 4 ebook

Hello all!

I just published a leanpub book on how to upgrade your Rails 3
application
to Rails 4. It covers all new features introduced in Rails 4 and
contains
the deprecated features as well. You can follow along with an included
upgrade checklist to see if you upgraded all breaking changes from Rails
3
to Rails 4.

You can get it over here: http://www.leanpub.com/upgradetorails4.
Feedback
and suggestions are very welcome. Thanks!

Cheers,
Philip