An example script, and accompanying Gemfile, to use for automating the Chrome mobile browser on an Android device. Tested on OS X Mountain Lion. Appium installed using node for CLI. If you don't have a fast android emulator, try genymotion...

android_appium.rb

# Connect your device or start your emulator before running this script

# make sure appium and chromedriver aren't started yet.
#`killall node`
`killall chromedriver`
#start appium server for chrome pkg and redirect stderr and stdout to keep terminal clean
#`appium --app-pkg com.android.chrome & > /dev/null 2>&1`
#prepare device
`adb kill-server`
`adb devices`
require 'fileutils'
require 'watir-webdriver'
require 'selenium-webdriver'

# The address and port of our Appium server
server_url = "http://localhost:4723/wd/hub/"

# Hash with information selenium webdriver needs 
capabilities =
  {
      'app' => 'chrome',
      'device' => 'Android'
  }

#Setup webdrivers to talk to Appium and mobile chrome and use implicit_waits to poll with long timeout to see if pages are loaded
driver = Selenium::WebDriver.for(:remote, :desired_capabilities => capabilities, :url => server_url)#, :profile => profile)
browser = Watir::Browser.new driver
browser.driver.manage.timeouts.implicit_wait = 30
puts "new ANDROID Watir browser object instantiated"

#automated browser code using Watir browser object and methods
browser.goto "http://saucelabs.com/test/guinea-pig"
browser.text_field(:id=>"fbemail").set 'bobbaxter@bobbaxter.me'
sleep 1

#screenshot code
%x(adb shell /system/bin/screencap -p /sdcard/screenshot.png)
time = Time.now.to_i.to_s
puts 'current directory is' + `pwd`
%x(adb pull /sdcard/screenshot.png ./images/screenshot.png)
FileUtils.mv('./images/screenshot.png', './images/screenshot' + time + '.png')
%x(adb shell rm /sdcard/screenshot.png)
`open images/.`

Gemfile

source "http://rubygems.org"
gem 'watir-webdriver'
gem 'selenium-webdriver'