I agree with you that Facebook has great potential as an evangelistic tool. Everybody and his brother/sister wants to be your/my friend, like friends of friends of friends. I have all but deleted everyone from my Facebook for now since I have a messages that everybody's friend says they have accepted my request to be their friend. I didn't request to be friends with all of these people. I suppose I don't know the ins and outs of Facebook well enough. But I think a church Facebook that members can take advantage of and let their friends know what's going on at their churches, may be a big plus for bringing people to the Lord.
I think every church should have a well-designed website in case anyone wants to find out anything about your church.
I do have a blog site I started recently which I think can provide much more content space for sharing testimonies, inspirational stories, Bible teachings, etc.
Check it out: 'God's Enduring Love'- Personal stories and testimonies of mission experiences in Northern Luzon, Philippines
http://heulu.wordpress.com