I believe it has to be renewed every year, although that may be just a formality. My understanding of the relationship is that your group becomes chartered by the Boy Scouts of America to run a scouting group. You actually "own" the group, and that comes with some liability as well. Here's a link to some information on the Boy Scouts website.
- Craig
Links in this post:
Boy Scouts website: http://usscouts.org/aboutbsa/bsaorg.asp