If I was to start a "Christian" social networking site called "FaithBook.com" (it's already taken...but suppose it wasn't) do you think that Facebook would take offense? Do you think they would have a leg to stand on to make me shut it down?
No, they would oppose only if you had the word 'Facebook' alongwith something else in the domain name.
I agree - FB doesn't own the name "Faith" - they can't do anything about it. btw-I like the name - did you start it up yet?
I have not started the site up. All descent versions of that domain are taken. I checked a few of them and they are mostly populated with lite sites that are more of a portal site than anything. I contacted one (the .com version) to see if they would be willing to sell, but I doubt the price they come back with will be reasonable.
Ultimately, it's about whether or not the domain name includes trademarked terms. You can check for trademarked terms at: http://www.uspto.gov/main/trademarks.htm
Faithbook should be allowed and facebook wont have the trademark to that, but you should check if any other company register that name.