Custom pre-made feedlists
You have a friend that doesn't use The Old Reader, but reads a lot of posts from a lot of blogs. You tell him to use The Old Reader, but he is a lazy person and isn't inclined to change his behaviour. You could use this feature to pre-build a feed for him, with the blogs you know he likes, and send a link to this custom feed to him.
With that link he could experiment the feed-reading stuff and, if he likes, he could just register and register that feedlist for his account.
Also, this could be used to share some feeds you read with other people who already have accounts, so they could just click on your custom feed link, check it and update their feedlists to include those new feeds you sent them.