You might also want to check out this Ezine article: Coaches - How Do You Get People to Follow You on Twitter? By Karen Skidmore
I think Twitter can be used effectively for devotions. Maybe it's a simple Bible verse or a thought of the day. I think it could be a useful tool to get the word out about the saving grace of Jesus Christ. I personally think it would be useful for me to I follow people who pour into my life. This is new territory for me, but I think Christians have a duty to use all media available to live with purpose and on purpose. God provides resources for us to do what He has called us to do.