das_download.rb

#! /usr/bin/env ruby
# usage:
# $ das_download.rb email password [download_directory]

require "mechanize"

class DasDownloader
  attr_reader :agent, :email, :password

  def initialize(email, password)
    @agent = Mechanize.new
    @email, @password = email, password
  end

  def screencasts
    screencasts_metadata_html.map do |html|
      next unless (meta = html.at(".title a"))

      title = meta.text
      url = meta.attr("href")
      download_url = url + "/download"
      description = agent.get(url).at(".details p").text.strip
      category = html.at(".category").text
      duration = html.at(".duration").text

      Screencast.new title, category, duration, description, download_url
    end
  end

  def run
    screencasts.each do |screencast|
      download screencast
    end
  end

  private

  def login
    agent.get "https://www.destroyallsoftware.com/screencasts/users/sign_in"

    if (form = agent.page.forms.first)
      form["user[email]"]    = email
      form["user[password]"] = password

      form.submit
      agent.pluggable_parser.default = Mechanize::Download
    end
  end

  def download(screencast)
    puts "Downloading #{screencast.title}"

    login
    Dir.mkdir(screencast.title)
    Dir.chdir(screencast.title) do
      File.open("metadata.txt", "w") do |metadata|
        metadata.puts "Title: #{screencast.title}"
        metadata.puts "Category: #{screencast.category}"
        metadata.puts "Duration: #{screencast.duration}"
        metadata.puts "Description: #{screencast.description}"
      end
      agent.get(screencast.url).save("screencast.mov")
    end
  end

  def screencasts_metadata_html
    login

    agent.get "https://www.destroyallsoftware.com/screencasts/catalog"
    agent.page.search(".screencast").reverse
  end

  Screencast = Struct.new(:title, :category, :duration, :description, :url)
end

email    = ARGV[0] or raise("Please provide the email address for your account")
password = ARGV[1] or raise("Please provide the password for your account")

DasDownloader.new(email, password).run

@jaredculp
Changed it a bit to work on Windows by replacing forbidden characters in filenames:
https://gist.github.com/elochim-siemasz/64edda44c2fcfc28d6b7eed9f78cd62c