I am not sure. The latest dashboard preview required that you be an accepted previous preview member, and have the preview app installed, then you had to go into the app an enroll your console into it manually. Basically, after NXOE, most/many/some/all we reset back to not being in the preview. Once you do that, in about 48 hours, it updated.
I think the biggies this update are the Apps/Games redesign, store (which is still terrible), and background music. Although, it seems like something else is coming that hasn't been released, yet, but, I am drawing a blank on it.
It's been fairly solid, which a few obvious hiccups. (Not being able to play any of my digital X360 games was kind of crappy for 24 hours...)