The staged rollout has been ridiculously slow. I had it on my business account before my personal one, well over a year ago I think. The biggest problem was that it was activated before all of the features were available, so either it would throw you back into an old-site page when you clicked on something, or you'd need to manually switch to the old design to find a certain tool or setting that wasn't yet exposed in the new site. As of the last month or so it looks finally like they've gotten all of the features I use onto the new site, and it definitely better than the early-noughties design of the old site.