I am not certain but I think the term was used to ensure that someone would raise the child in the ways of the Bible. A sort of Christian insurance. Obviously not the same imperative now.

I know people who take that role very seriously. My best friend considered asking me to be his kid's godfather, but I wasn't sure I should.... They take the role seriously, and so did I. I more worried about getting caught up in family stuff if anything were to happen. In the end I'm just Uncle Ben... but it's a pretty cool title.

I've never been asked. I doubt I'd do it, but I'd consider the circumstances.

It is not. As a legal guardian you are allready a civil godparent. As far as the religious aspect of a godparent you are responsible for their spiritual guidance as well. I am the godparent to 2 of my nieces and I have guided them spiritually but by teaching them religious tolerance of both the many different believers and also the different non believers. One neice is now an atheist and the other a Christian (from catholic).