The following are a few simple examples of how you
could use the Xbee as an RF trigger. Links are provided to each examples own blog post;
I have published each example in a new post so that for ease of use. I hope this helps you get started quickly or help you decide for yourself whether Xbee is the right tool for what you are intending to build yourself.
Please comment on any posts you found particularly useful and provide links to your own Xbee, RF or Arduino work.