Today I checked one of my Gmail accounts and found that Google automatically added tabs to sort emails. Now, next to the "Primary" tab, you can see "Social Networks"-related emails (Reseaux Sociaux in French) as well as "Promotion" for mostly any newsletter you may have subscribed to. You also have the possibility to add categories and drag and drop messages from a tab to another. Although this is not really news (see this article from The Next Web), it's the first time I see it and I haven't seen it rolled out on my other Gmail accounts yet.
What are the benefits?
It won't replace the primary email stream with all your emails ordered by date. However, it's pretty nice to be able to see all emails from social networks, for example. It's too new to tell how useful it is to me. You're welcome to comment if this change is life-changing to you.
You cannot custom-create new tabs. You can only choose from pre-formatted categories chosen by Google. I noticed that some of the blog newsletters I subscribed to --which have no commercial character-- were classified by Google as "Promotion". I guess Google has yet to fine tune these, or let users do the fine tuning (moving messages from one tab to another) and learn from them.