Currently friends can see each other's "shared" posts, but sometimes there is a specific post that looks interesting to a specific friend; it would be nice to be able to notify that one person about that one post.

For example, today I saw a post about 3D printers in one of my subscribed feeds, and I would like to let my wife (who's also a user of The Old Reader) know about it.

I could e-mail her the post's URL, but it would be much simpler if there was a "recommend to user" option, which would in turn make the post appear on a "Recommended" section on her account.