Canon EF 70-300mm f/4-5.6 IS USM Lens for Canon EOS SLR Cameras

The short version:

Pros:
The optical quality is great, the speed is terrific, and it compares well to the 70-200mm lens that people like to say blows this out of the water (I believe they are wrong - but we will get into that later) and finally, the price cannot be beaten. Buy it.

Cons:
No hood, extends as it zooms, and the quality of the picture in low light situation lessens a little.

The long version:

I am writing this in simple terms. I found several, several reviews on this lens but they were all in technical terms and leaves you scratching your head a little. So, if you are like me maybe this review will help you.

I bought this lens a couple months ago from US1Photo.com (check these guys out. They regularly have significant sales and terrific customer service). I use this lens with a Canon 40D.

I take several types and styles of pictures so I needed a lens that would do the best job at several... Read more

After debating between this and the 70-200 L series I decided to purchase this lens. I have been pleasantly surprised by the results. I also own the 17-85 and the 50mm 1.8 lenses and I have found that I have gotten the "most pleasing" results from this lens. The pictures have been very sharp from my 20D - even in the 200mm - 300mm range. I've also been happy with the quality of the bokeh.

The primary drawback I see is that the AF tends to hunt a fair amount when confronted with low contrast images. That being said, I used it for some flying bird shooting at the wildlife refuge and was surprised to see how many of the shots were in sharp focus. However, it was a little bit of all or nothing. Several shots were also wildly out of focus. Since the lens is fairly slow to focus, you never know what you're gonna get with such a fast moving object against the distant sky.

I had much more consistent results when shooting soccer, softball and football in the park... Read more

I bought this lens as a replacement for the earlier 75-300mm IS lens. I was generally happy with that lens, but it had definite limitations - I needed to shoot at f8 or f11 and bump up the ISO to get a decent shutter speed.
This new version seems sharp at full zoom even wide open, allowing me to use a lower ISO setting. Size is similar to older version, but the IS seems more effective - looking through the lens when it kicks in you can actually see the image become more stable and less shaky. I got this over the Canon 70-200 f4 L because of the extra reach, smaller size (slightly) and the images I've seen from both are very similar.
UPDATE: There have been reports of soft images when using this lens in a verticle orientation - however I have not experienced this on my copy. I'm happy to say that after months of using this lens, I still consider it great.