Interesting. I have "labels" setup in gmail that match this system very closely, and i use "rules" and manual filtering to deal with it. I wonder if Gmail will automatically mark the emails for the right tab accordingly or if there'll be some scope to customise/tune the system.
formalizing and automating. having your messages automatically filed into one of those tabs (without having to set up any rules) is a lot more exciting than the fact that the tabs exist.
People who want their email under control already have something similar - for instance, I have filters and labels and folders for Newsletters and offers, one for Family and friends, University and so on.
People who haven't taken control of their inbox yet won't be bothered to do that now.
They've actually done this for a while without any user interaction. They automatically have setup forums, notifications, and bulk labels for me. They've just moved them too the top. Hopefully they've refined them too cause they never worked too well for me.
This won't help me. The only pain point I experience in my GMail workflow is the inability to mark-as-read or delete emails from my status tray. I end up opening one-line emails and spam just so I don't have to track them down and mark them as read later.
Either way, it's a welcome step forward.