I keep reading that Google Apps allows shared contacts and that it does not allow shared contacts? Why two opposite statements?
Because its sharing is not what most people expect when talking about sharing.
What you can share is the list of users in your domain. Not the list of partners/clients/prospects. And this is what most people (me included) expect.
Shared contacts, but not shared addressbook. And this is deeply annoying. This is the number one feature request for Google Apps (closed, read-only survey, sorry). Hopefully, someone at Google will investigate upon this.