If I may, let me share some of the things, I think, I have learned and some of the exchanges I have had with Eric...
First, I do not believe there is any easy or cookbook way to rationalize what your camera histogram shows and how far you can push ETTR to not blow highlights in LR. Each camera system and usually each camera is going to be a little different.
You need to learn how you camera is going to work....i.e. a calibrate it. Lee Varis, in his book 'Mastering Exposure..." (or a free PDF extract from it) shows how one can calibrate it...i.e. how much room do you have after you hit the blinkies and right side of the chart. This, obviously, needs to be done in oncert with the raw converter you are using.
One thing I noticed, and is cussed with Eric, is that 2010 and 2012 are quite different in what hey tell you about over exposed highlights. In 2010, if you have red indicators of over exposure in your image, that does not tell you if they are truly blown or just that the other settings have pushed them there. Only later, if you try to recover hem will you find that some are really blown and have lost all, or most, detail.
I have found 2012 to be quite wonderful in this area. At the initial default settings, the only areas which show red are are those that are totally or partially "blown", i.e. misinterpret detail. This makes it much easier to determine if these areas are significant to the image...and if so...to not even bother to try to work on the image as these areas will never look good and will usually at best provide a silvery or grayish area with no texture.
Anyway, this was first on my list of "likes" about LR 4. The more I use it, the longer the list becomes.