Pros: My first L lens and is sharp. I had it exchanged once and the second is really good. Focal length is right for walk around to parks and play grounds in sunlight. I already knew its slower aperture and lack of IS and no complains on that. Good bokeh on longer side.

Cons: My first copy was not good at f/4, but 1-stopped down, its is razor sharp but I returned for an exchange and got a fantastic(may be it is how it is) lens. No cons for me so far.

Other Thoughts: This is my first L, but I got chance to try with other L lenses including 100-400. But so far this is one of the sharper L lenses. Comparing it with Canon 50 f/1.4, Rokinon 85 f/1.4(boken king), Canon 100mm f/2.8 macro(non-IS) and others for sharpness on 40D, nothing can beat my 50mm f/1.4. May be I got a better/best copy.

Huge disappointment with first copy. 28-135 gave better results than this lens wide open(f/4). Since it was only "Replacement/Exchange" policy, I could not return and then decided for exchange. Thank full to Newegg, no questions, just replaced and I will keep this copy. It is as sharp as the first copy at f/5.6, wide open(f/4) and there is not that much improvement stopped down as it is already sharp. I now have 17-200mm(27-320) with primes covering the low light and good portrait focal lengths.

Pros: Internal zoom, takes great photos, the low f stop makes shooting in low light conditions easier (focus will become smaller), fast auto focus, Glass quality is great, tripod collar not needed

Overall a great lens.

Cons: Note really a con but I wish it were IS.

Other Thoughts: I have been using the lens for years and it has always been good to me. Takes great photos, price has actually gone up since buying.

Pros: Auto focus is fast and just like the f/2.8 IS. I took photos of a mountain bike race, and the auto focus was spot on (just make sure it's set to continuously focus).

Quality of the glass is totally L series material.

Light! Lighter than the Canon 16-35mm f/2.8 USM lens. You can run around with it, carry it in your Camelback while mountain biking (which I did). And you DON'T need a tripod collar--that's why it doesn't come with one.

Looks awesome on my T2i, where the f/2.8 was massive and the T2i looked stupid.

Cons: You will need to get used to, or learn how to use flash. In those indoor areas, or if the sun is covered by the clouds in a shadowy area under trees, you will need flash. An external flash with a defuser should help with that.

No Image Stabilization, so your shutter should be around 1/160 or higher (again, why flash is needed in those dark areas)

Other Thoughts: I know flash flattens everything out, but for sports, it's fine. I like to defuse my flash, but what ever you do, don't cover half of the on-mount flash with electrical tape...because it starts smoking and smelling really bad.

Pros: Outdoor shot is amazing. Very high quality. Indoor focusing a little slow.

Cons: Wish that it's 28-200mm instead of 70-200mm to be my all-in-one lens.

Pros: Very good quality lens. Fast zoom. Good aperture throughout zoom range. Sharp pictures. Internal zoom.
Much lighter than f2.8L.

Cons: No really Cons.
It is a little bigger than other lower performance lenses but the quality is worth.

Other Thoughts: Excellent lens for outdoor sports.

Pros: constant aperature, solid construction, decent price, good zoom range, canon colors

Cons: resolution not on level of primes, no tripod collar

Other Thoughts: I purchased this mainly for studio portraiture and maybe I've been using the 135L and 85 f/1.8 too long but this is not to those levels of resolution, particularly soft focus in the 80 to 110 range at f/5.6 to f/14. It's still very good but I was hopeful it would be more prime like. I mean the 135L and 100 f/2.8 macro don't need any sharpening of any sort, eyelashes are always perfect, unless error on my part. I just don't quite get that with this lens. Of course, those two lenses happen to have some of the best sharpness out of any of canon's glass including the 85 f/1.2. Thus if I came from using non-L zooms I might be mightily impressed but I am a prime guy and primes, even non-L, generally beat up the zooms, even the L's.

Pros: Sharp, Focal Length Range, Constant Maximum Aperture, Fast Focusing, Value

Cons: None

Other Thoughts: This is easily one of the best bang for your buck lenses available for Canon DSLRs. It offers L class optics and build quality for relatively little $ and considering the focal length, this lens is not that large or heavy. True, image stabilization would be nice but this model costs half as much as the IS version and you should use a tripod for low light shooting anyway.

Pros: This lense is remarkably well balanced and its' optical performance is exceptional. I should have purchased this lense years ago. I am amazed at the clarity of my images and the saturation of colors in my images.

Cons: Now that has merit to mention.

Other Thoughts: I have used this lense on a Canon digital camera that has been converted for IR B/W and I love the results of my treks out shooting with this combination. For more precise control the IS function would serve me better in lower light hand-held shooting.

Pros: First off this is my first lens to buy for my dslr body. It is simply perfect! The touch on the focus and zoom ring feels very good and solid, and after a while the zoom ring gets a little easier to move but not too fast. This lens is tac sharp, ive taken pictures where i could see every single pore on a persons face, and every single detail of the ball inside of a dandelion! The zoom range of this lens is not made for birding unless your about 5-10 feet away from them and that wont fill up the full frame at 200mm (320mm at 35mm) The range is excellent for baseball games (the batters) and for any type or portraits! The f4 is actually a decent speed, and not having the aperture change througout the zoom is very nice to have too. The included lens hood is awesome and the bag that comes with it helps a lot too. The 1.2m or 3m close focus range button definately helps when shooting things through fences. The bokeh is definately awesome and color reproduction is almost perfect!

Cons: My camera with this lens on now costs more then my car.

Other Thoughts: The learning curve for getting this lens steady is about 1 day, which was okay with me. You get a lot of attention in public because the white finish attracts people very easily. I recommend getting a rocketblower or something to keep dust off of the front element.

Pros: Sharp, very fast focusing, ring USM, lightweight.

Cons: No IS, not a very fast lens.