I saw a guy in the mines write a note titled "A Cautionary Tale" about someone who knocked on his house and, after letting her in, proceeded to take all of his stuff.
This is clearly a problem, because it abuses goodwill. What if a person wants to let someone in their house from afar just to check it out? Are we going to become scrooges because of the potential abuse here? Glitch doesn't seem like that type of community. Most of the solutions I can think of aren't very good, but I can think of a few that might solve this problem:
1. Have an option for enabling and disabling item-sharing.
2. Prompt the user if a person wants to pick up an item from their house. This could be done like a firewall, with "just this once" permission and with "forever" permission.
3. Allow the user to completely block a person from repeated knocks. I had a guy knock twice -- he was clearly gunning for my stuff.
4. Only allow selected users to know when we're online or to be able to knock on our doors.