I debated about the price rating but I must say, I owned the non-IS for years and shot a whole lot of indoor sports, concerts, and other indoor things where the non-IS was "almost" there, but not quite.
And this is why I decided to purchase the IS version. I sold 2 lenses, the 135/2 L and my 70-200 non-IS, in order to grab up a new IS so I could check out the difference and in hopes that the IS would offer me that tiny "edge" that counts.
I've had the lens for a month now and have shot a basketball tournament and a xmas concert. My keeper rate is about 98 percent where my keeper rate with the non IS was about 70 percent at "most" and it still lacked something that I cannot explain.
I am amazed with this lens, and the IS definitely makes a HUGE difference in my shooting. Again, I owned the non-IS, a sharp copy, for 3 years. The IS version could be compared to the high jumper who "almost" makes the jump. The non-IS is the "almost" whereas the successful jump comes from the IS.
I'll die before I sell this gem! Plant it with me when I die.