I have the 70-300G mounted on my A700. Here are my thoughts of this lens.
This lens, compared to the 70-200G, is surprisingly lightweight. This makes it a great telephoto lens for backpacking. The image quality is everything you wished for: sharp wide open at all focal lengths, lack of aberrations and fringing wide open, even sharpness across the frame, great contrast, and little distortion. It is the best 70-300mm money can buy (and possibly the most expensive compared to Canikon equivalents). AF is practically silent, fast, and accurate. The focus limiter is handy if you're into fast action photography.
I also like the minimum focusing distance because it gives you the opportunity for some close-up work and gives you a very nice defocusing effect with its 9 aperture blades (as opposed to 7 in cheaper lenses).
Now the downsides:
- plastic body (although it is high quality and keeps the weight down)
- finicky focus ring, it is almost too easy to turn and manually override after AF is confirmed
- dust pump, the end of the barrel does extend as you zoom in and out, and I have a couple of dust particles in mine already
- relatively slow aperture
- massive hood that draws attention (although from my unscientific tests it does not make a difference to image quality)
- you will notice decrease in battery life because of the power requirements of the SSM motor
I highly recommend this telephoto lens if you do some traveling, and have some cash to spare. If you're interested what you can do with this lens, I took some shots with the lens, they are indicated on my flickr stream: http://www.flickr.com/photos/31973354@N08/
. Note that I did not correct any distortions and colour fringing in any of my photographs.