Lessons learned from a weekend with the exotic:
Holy subject isolation, batman.

I was shooting pictures in a crowded dressing room that looked like studio stuff. The backgrounds were simply creamy, colored smears. I ended up stopping down in many cases simply to give some sense of location to the pictures.
Focus points are incredibly critical at f/2. You have to choose manually, and put the focus on an eye, or else it will be soft. DoF is simply too shallow to let the camera choose some random spot on the face.
Incredible performance, shooting almost directly into the sun. Only 2-3 pictures out of several hundred showed any flaring, loss of contrast, etc.
VR works. Able to get solid shots down to about 1/40th of a second. Unless the subject was moving.
Confidence. I probably didn't accomplish anything that couldn't have been done with a 70-200, but I tried a lot of things that I might not have otherwise, and many of them worked. It just begs you to push it to the limits, and expand your thinking a bit.
I like it far better on a full frame body for this type of event. I understand it was designed as a DX replacement for the 300/2.8 but 300mm equivalent is longer than I needed or wanted.
Shot the day primarily with the 24-70 and the 200. Number of times that I missed having 71-199mm available:
0
It's a huge beast, and definitely draws attention. Even got a raised eyebrow and a comment or two from the staff at the banquet hall, who see probably 15-20 weddings a month.
And returning it this afternoon was sweet, sweet sorrow.
Overall:
I certainly won't be renting one every time, due to the price tag, but wow. I'll be back.