Move everything on your desktop into ~/Dropbox/Documents/Desktops/<yyyy-mm-dd>/

archive-desktop.rb

#!/usr/bin/env ruby

require 'FileUtils'
require 'date'

def create_dir_if_necessary(path)
  Dir.mkdir(path) unless File.directory?(path)
end

desktops_path = File.expand_path("~/Dropbox/Documents/Desktops")
create_dir_if_necessary(desktops_path)

today = Date.today.strftime('%Y-%m-%d')
today_path = File.expand_path("#{desktops_path}/#{today}")
create_dir_if_necessary(today_path)

FileUtils.mv(Dir.glob(File.expand_path("~/Desktop/*")), today_path)