DEPRECATION WARNING: This method will become a separate plugin when Rails 2.0 ships.

Example:

# Controller
class BlogController < ApplicationController
  in_place_edit_for :post, :title
end

# View
<%= in_place_editor_field :post, 'title' %>

For help on defining an in place editor in the browser, see ActionView::Helpers::JavaScriptHelper.

Methods
I
Instance Public methods
in_place_edit_for(object, attribute, options = {})

Source: show 

# File rails/actionpack/lib/action_controller/macros/in_place_editing.rb, line 23
def in_place_edit_for(object, attribute, options = {})
  define_method("set_#{object}_#{attribute}") do
    @item = object.to_s.camelize.constantize.find(params[:id])
    @item.update_attribute(attribute, params[:value])
    render :text => @item.send(attribute).to_s
  end
end