I have noticed that in Rails 3.2.2, all actions are being processed with */* format. So the question is: what means */* ? And why it is called by default (every time) ?

Because there are two processings for one action:

Started GET "/" for 127.0.0.1 at 2012-07-07 22:50:22 +0200
Processing by MainController#index as HTML

Started GET "/" for 127.0.0.1 at 2012-07-07 22:50:22 +0200
Processing by MainController#index as */*

I have tried to set:

  respond_to :html

  def index
    @posts = Post.all
    respond_with(@posts)
  end

But the same problem still exists.