I'll also cast my vote for 100 IRE (not percent :-)

Please correct me if I am wrong, but I seem to recall that DV goes up to 120 IRE, but it won't show much through a standard TV signal. I saw a chart that goes to 120IRE before and I can see more detail in the highlights on a computer monitor than a TV. This means that there is some detail in the highlights, but it won't show on the TV. You could use some color correction to change the gamma to bring some of that detail back down to broadcast levels. Regardless, don't have a great deal of zebra bars at 100IRE unless you are in a situation where you need to let background blow out so that faces can be preserved.

DV erov 8 bit is digitized from 16 to 236, while 8 bit goes from 0 to 255, that is probably why some people are talking about superblack or superwhite value or consider that DV goes up to 120IRE.
Since most of codec are clipping to range 16-236, it is pretty dangerous to count on these extra values

Zebras are a powerful tool, and indeed the only tool we usually have to determine exposure in the field.

I use all of them - 70-100%, but mostly 85 and 100. I use 85 for broad highlights on caucasian faces, and may let shiney face highlights go to 90-95. Sometimes 75 for broad highlights on people of color, depending. 100 is very handy as mentioned above for determining what will be blown out to white, usually it is only specular highlights that I'd want to see at 100% (point-like reflections off of shiney objects).

Racking through 70-100 is a great way to see whether a background is evenly lit, especially a chromakey background.