I'm fairly new to drupal, and am looking to switch from another CMS we are using, but I need to make sure we have some different options before I switch. As far as single-sign on, is it possible to present a list of all sites on a multi-site installation when creating a new user, and then only give users access to certain sites when they login? Still taking advantage of the single-sign on portion, but just not logging into all of the sites.

Thanks!