Summary: I use this lens mostly for sports photography, but it's actually great for portraiture too. I've used it for a few senior sessions and the bokeh is amazing. Super smooth, super sharp, even wide open. Stop it down to f/4 and it's even sharper! For sports, I mostly shoot football, softball, and baseball with this lens, but you can actually shoot the far end of the court in basketball as well. I can't overstate how good this lens is.
Excerpt: This lens is simply phenomenal. This is my first step into the "big whites" and I am sure will be in my collection for many years to come. Optically, it is practically flawless. The sharpness is out of this world and unlike any other lens I have had the pleasure to use and own (such lenses as the 24-70 II, 70-200 II, 35L, 85L, 135L, 300 f/4L, 400 5.6L…. And many more). The 300mm f/2.8L II is in a league all its own.
Pros: Consistent Output, Durable, Easily Interchangeable, Fast / accurate auto-focus, Image quality, Indented Tripod Ring, Is Performance, Nice Bokeh, Rugged, Strong Construction
Excerpt: You can count on this pro grade canon glass to get your money shots 99.9% of the time. I have 300mm is/vr lenses from both camps, and I would say that this canon IS II version takes the cake, as it is both lighter and IS mode 3 is an evolution of the IS system. The new front cap is great, as I no longer feel the need to buy a don zeck cap.
Summary: I can only enthusiastically agree with the other 5-star ratings here. It's an amazing lens. I considered the 400mm and rented it for a weekend to try it out, but it's just too big, too heavy, and much more expensive. I can actually hand-hold this lens with the 2.0 tele-extender attached and get razor-sharp images at 600mm/F5.6. I was worried that the autofocus would hunt in this configuration, but my 5DIII had no problem nailing it every time.