Blog friend protocol?

I have come across a few random blogs where people have befriended each other through the blog. Some of them have gone as far as getting married eventually. Another form of digital romance I guess. This makes me wonder about the protocol to befriend someone through your blog. How long is one supposed to wait before you make the next move? What is the next move? I think it would be facebook. I should try it, but then again most people who comment on my blog already know me. Falling for someone through a blog is too far fetched for me. One of these days I will figure out unwritten laws of befriending people on blogs. It should go up on the 'Useless things to do in this year list', very soon.