Information sharing is a hard problem in general. Limited information sharing is actually even harder than sharing with the general public.
At a recent presentation in Brisbane, Pia Waugh noted that for Australian government departments, getting permission to share information online is only a little bit more work than getting permission to share information with one other department. By doing that little bit of extra work to make the information available to the Australian public, they also make it available to every other government department.
That's a powerful benefit, and something the enterprise world would do well to pay attention to.