Problem:

gistfile1.txt

ActionController::RoutingError: No route matches {:action=>"destroy", :controller=>"users", :id=>#<User id: 1, first_name: "Demo", last_name: "User", email: "demo@example.com">}
	from /usr/local/lib/ruby/gems/1.8/gems/actionpack-3.0.0.rc/lib/action_dispatch/routing/route_set.rb:398:in `generate'
	from /usr/local/lib/ruby/gems/1.8/gems/actionpack-3.0.0.rc/lib/action_dispatch/routing/route_set.rb:450:in `generate'
	from /usr/local/lib/ruby/gems/1.8/gems/actionpack-3.0.0.rc/lib/action_dispatch/routing/route_set.rb:478:in `url_for'
	from /usr/local/lib/ruby/gems/1.8/gems/actionpack-3.0.0.rc/lib/action_dispatch/routing/url_for.rb:132:in `url_for'
	from /usr/local/lib/ruby/gems/1.8/gems/actionpack-3.0.0.rc/lib/action_dispatch/routing/route_set.rb:195:in `user_url'
	from /usr/local/lib/ruby/gems/1.8/gems/actionpack-3.0.0.rc/lib/action_dispatch/routing/polymorphic_routes.rb:114:in `send'
	from /usr/local/lib/ruby/gems/1.8/gems/actionpack-3.0.0.rc/lib/action_dispatch/routing/polymorphic_routes.rb:114:in `polymorphic_url'
	from /usr/local/lib/ruby/gems/1.8/gems/actionpack-3.0.0.rc/lib/action_dispatch/routing/url_for.rb:134:in `url_for'
	from (irb):1

project.rb

class Project < ActiveRecord::Base
  has_many :memberships
  has_many :invites
  
  validates :name,        :presence => true
  validates :description, :presence => true
  
  attr_accessible :name, :description

  has_friendly_id :permalink, :use_slug => true
   
  def permalink
    "#{description}:#{name}"
  end
  
  def normalize_friendly_id(string)
    string
  end
end

routes.rb

MyDevApp::Application.routes.draw do |map|
  root :to => 'home#index'
  resources :users
  resources :projects, :only => [:new, :create]
  
  get ':project_id' => 'projects#show', :constraints => { :project_id => /\w{3,24}\/\w{3,24}/ }, :as => 'project'
  put ':project_id' => 'projects#update', :constraints => { :project_id => /\w{3,24}\/\w{3,24}/ }, :as => 'project'
  delete ':project_id' => 'projects#destroy', :constraints => { :project_id => /\w{3,24}\/\w{3,24}/ }, :as => 'project'
  get ':project_id/edit' => 'projects#edit', :constraints => { :project_id => /\w{3,24}\/\w{3,24}/ }, :as => 'edit_project'
  
  scope ':project_id', :constraints => { :project_id => /\w{3,24}\/\w{3,24}/ }, :as => :project do
    resources :memberships, :path => 'members'
    resources :invites do
      get :accept, :on => :member
      get :deny, :on => :member
    end
  end
end

user.rb

class User < ActiveRecord::Base
  has_friendly_id :permalink, :use_slug => true

  attr_accessible :first_name, :last_name
  
  validates :first_name,  :presence => true
  validates :last_name,   :presence => true

  def permalink
    "#{last_name}/#{first_name}"
  end
  
  def normalize_friendly_id(string)
    string
  end
end