I did have a chance to try out 4 some last night. I still do not know about the tone curve baking in the old medium tone curve as linear, I will have to see how that behaves more. It seems like curve changes are a lot more sensitive than they were with the old linear, and it is really easy to overdo it, but not sure yet.
On the new exposure and 4 different tone sliders, it looks like it works reasonably well. I was able to recover some highlights in some particularly tough photos that the previous process and controls had problems with. I had to go to spot adjustments in LR 3.6 for those.
There are some unexpected interactions between whites and highlights (and blacks and shadows). I would try pulling down the whites to recover the top end and have little effect, but if I also pulled down the highlights, then the whites slider did have an effect. So, I do not think the zones and their controls are as pure as presented in the UI. Not complaining, mind, but interesting.
There are a few minor glitches with how LR 4 works with the Nik Software plugins in terms of where the edited photos end up after exiting Nik, but otherwise, the interaction seemed fine.
Doug