Tom Tate, writing at the AWeber blog:

With tags, you can apply specific tags (or labels) to each of your subscribers (based on things like whether they are a customer or prospect, where they signed up, interests, geographic location, etc.,) in order to send targeted broadcasts and trigger campaigns.

This is a feature that AWeber’s customer base has been awaiting for years. This is huge. In the past, the only real way to segment users was to create new lists, which lead to lots of duplicate contacts. Since AWeber’s subscription model is based on your number of subscribers, this meant that the more times you segmented your users, the more expensive maintaining your account became. With tags though, there isn’t a reason to ever need more than one list.

True story: about six years ago I put together an article about the superiority of AWeber over MailChimp. AWeber’s CEO liked the article so much that the company reached out and sent me a T-shirt. Over the years though, MailChimp has become a fierce competitor with a stellar interface; and meanwhile, AWeber has fallen behind in terms of a coherent design. But its core product — sending emails with an untouchable deliverability rate — is still intact.