This lens replaced the 70-200mm IS L f/2.8 II in my bag for a trip to Chiapas, Mexico.
All during the trip, I found the ease of use and extra reach over the 70-200 to be an advantage. The lower weight was also noticed over a series of long days.
I did get a little tired of other photographers wanting to hold it and look through it.
Now, when I go on a trip that requires a lens with some reach, it will be the 70-300. It performed well for me, and I am glad I purchased it.
Since the trip, I have continued to use the lens at home. It is nice to have that extra reach. This lens gives me hope for a nice 200-400 soon.