Tags are essential. Think about this: a user saves this link to a list of stories about Pocket. He also collects links about Mozilla's management, so he puts it on a list of stories about Mozilla. Then he remembers that he wants to talk about this link with a friend, so he adds it to a list of links he wants to share with his friend.
According to "lists," he has to choose between one of those three lists, while with tags he can use all three. Search does not replace tags, and neither does having to manually type keywords into the description field.
Leaving out tags is a fundamental oversight. I would never consider using any service that didn't have them.