I compared this lens to an equivalent Tamron (I believe it was), and this lens is far superior. Extremely fast and quiet focusing. The f2.8 is greatly enhances my ability to shoot sports indoors without use of flash. The lens is heavy, which is where the monopod ring comes in very handy. If you are a weekend shooter, the cost and weight are probably not worth it, but for those who are more serious or shooting professionally this lens will quickly pay off.

As a professional wedding photographer, I'm always looking to get the best in quality and performance. With this lens, you get the best of both worlds. I've rented and used this lens about 5 times, and the images it produced were astonishing. So much so, I had to just splurge and buy it. Although this is a zoom lens, the images are very close to prime quality. If you're looking for sharpness, this is as close as you'll get to prime lenses. The 70-200 range is very convenient for portraits and tight shots. I can stand in the back of a low lit church, turn the IS on, and get spectacular shots at f/2.8... handheld. Mount this on a tripod or monopod, and you can get tack sharp images in almost any situations. The IS works really well, and you can feel it working. You can easily get sharp shots at 1/60th of a second, and very usable images at 1/30th. [...]
Most copies are excellent, but it's possible to get a soft copy (canon has a known quality issue with some of their lenses). The 1st copy I ordered from amazon was a bit soft wide open, but I returned it and exchanged it for a much better copy. They even refunded me the money it cost me to insure and send it back. As with any lens, it's best to test it out in person... but you really can't beat amazon's price. The best thing to do (if you can afford it) is to order 2 or 3 of these lenses, test it out, keep the sharpest, and return the others. I still don't have the sharpest version (the one I rented was), and this is the only reason why I didn't give a perfect rating.

If you're considering getting this lens, then you probably already know why this is canon's best zoom. Supposedly the f/4 is a tad bit sharper, but the 2.8 more than makes up for it in low light situations. All I can say is, it definitely lives up to the expectation. This is THE most convenient lens in my bag, and it practically sticks to my 2nd camera body at all time. If you need to get one zoom, then get this without a doubt.

I've been using this lens on my Canon 40D for about a week now, as my #2 shooting lens for general work walking about town when I need to reach out a bit farther than usual (my #1 lens is a 24-70mm f/2.8L USM). I've used it for architectural detail shooting, some portrait work, some entertainment-subject shooting in low-light conditions, even some quasi-macro shooting. This is easily the best long EOS lens on the market, and at Amazon's prices, it's one of the best bargains in photography.

The glass is perfect, the IS and USM mechanical works are super-fast and silent. And it's absolutely astounding how the image-stabilization voodoo can allow me to hand-hold shots in moderate light that before would have had be running for my tripod. And that cavern of an aperature lets in an *enormous* amount of light.

Add the 2x extender and you have a 400mm to 640mm f/5.6 image-stabilized supertele lens, screw in the 500D close-up diopter and you have the next best thing to a dedicated 70-200mm macro-zoom. Quite the versatile lens...

About the only thing that may queer the deal for some shooters is that the IS works will draw more juice from your camera battery than you may expect; I wound up using a BG-E2N grip with two 511A batteries whenever I'm using this lens, just for safety's sake. But OTOH it gives me a better grip to control the lens by; it certainly is a bit on the heavy side, at just under 3-1/2 lbs.

Also, you really do have to keep tabs on your depth of field when shooting this lens wide-open to keep your subject in proper focus; the DoF at f/2.8 is razor-thin! But that's what wide-open aperatures do

All things considered, though, I couldn't recommend this lens highly enough.

This the first 'big' lens I've purchased in my 8 years of learning to get good photographs of subjects I enjoy. It seems to fulfill the need to have the ability to capture subjects well at a distance. I bought it to help get good shots of softball players. Since I play on a team, I am able to be on the field during play consequently wish I'd purchased Canon's Canon EF 24-70mm f/2.8L USM Lens instead. This lens (24-70) would have given me that little bit more distance ability than the f/2.8 17-55 mm I normally use. Looking at the photo's metadata taken with the 70-200 mm lens I find most interesting, I see where 95% are taken at 70 mm. I need to say that only about 300 images have been captured with the 70-200 mm, I'm sure as time passes I should be able to learn to use it much better. (For what ever it's worth - most photos taken with the 17-55 mm lens mounted on a Canon 40D were taken at the 40-50 mm settings. The reason for four instead of five stars is mostly the weight.)

There are plenty of good reviews so this one will be a short summary:

Pros:
- Sharp images accross zoom range
- Effective image stabilization
- Fast, precise USM autofocus
- Built tough with moisture and dust seal

Cons:
- A little heavy but considering lens size this is minor
- A little on the pricey side

Other:
- Comes with hood and soft storage case
- Overkill for student/amateur like myself