So how are google deciding which emails are important? That's the only new thing with this Priority Inbox - you've been able to do this for some time with filte

So how are google deciding which emails are important? That's the only new thing with this Priority Inbox - you've been able to do this for some time with filters and multiple inbox (labs feature). I want to explicitly filter things that are important to me. Even this article recommends that. Feels like Priority Inbox is just nice packaging/marketing on the multiple inbox feature + auto-filtering on your friends.