I have had this lens for over 2 weeks now. Here in Canada I paid $1600 + tax.
Honestly I believe that if the tripod collar was included, it would be worth that amount of money. It is quite frustrating that Canon not only does not include it, but sells it for a ridiculous price, and I know I'm not the only one feeling this way.
At the store, I basically tested this lens and the new Tamron 70-300 side by side. For more than three times cheaper than the Canon, the Tamron was surprisingly good, but the Canon was better. The autofocus is really fast and silent, the IS is really effective and barely noticeable, it's built like a tank, and it has a zoom lock.
I know some people are complaining about where they placed the zoom and focus ring, but it really makes sense when your handholding the lens at 300mm, it creates a better balance, and feels more stable than if your were zooming to 300mm and handholding with your hand just in front of the camera.
The optical quality is excellent, and corner sharpness is actually quite good. Obviously it's not perfect at 300mm, but it's actually pretty sharp.
The reason I decided to go with this lens is because I work with a 5D Mark II. If I had a 7D or any of the cropped sensor EOS, I would probably have gone with the 70-200mm f/4 IS.
In my opinion, IS is a must now so the 70-200mm f.2.8 non IS was not an option, and the new IS II sells for a ridiculous $2500 here so no thank you.
The reason I didn't go with the 70-200 f/4 IS is because it's just not enough reach with the full frame, and I find that it's really annoying to always reach for a teleconverter, maybe miss a wildlife shot and get more annoying dust on the sensor.
Being mostly a nature photographer, I encountered one little problem with the lens when used on a tripod, which brings me back to the tripod collar. When I zoom in between 200-300mm, the lens is harder to focus in live view mode because when I'm manually focusing, I'm creating a slight vibration, which makes it harder to focus really precisely at 5x and 10x magnification. It's not that big of a deal, but I take more time to make sure that my focus is right where I want it to be.
So I will be saving my money and eventually purchase the tripod collar.
I am really happy with the lens and am confident it will get a lot of use for many many years.