This shouldn't be an issue with CB, as we auto-authorize users who sign up through Facebook. Do you have some plugins that require authorization or some other component that has it's hands in the user table (and needs to authorize users)?
As for Virtuemart, we just completed CB support, and haven't started on integration with other components. If a user registers through CB on your site, is that information being ported over the VirtueMart table? If so, how? Is it through a plugin to CB, to VM, or is it integrated into one or the other components?