Personally, when I join a new site, then the site itself sends me an email, I ignore it. When I joined Mibba a couple years ago, new members were displayed on the home screen, so they had a ton of comments and messages welcoming them. I miss that. I think a thread would get out of hand quickly. Either a welcoming committee or just adding a new members section to the home screen would be best, in my opinion.
I remember the new member section. I fully agree with your idea, it should be brought back