James, yes there are problems with every lens. But it doesn't mean you will encounter them even if they are present. You use the lens for landscape, but never shoot architecture, so how would you encounter the distortions?(If the lens doesn't have super barrel distortion, like a fisheye..)
I can't comment on any issues yet, i just shot the boring brick wall images, and some images random snap shots.
This lens has perfect balance on the 5dm2. On Canon rebels the weight is leaning forwards, but balance can be improved with the use of a battery grip. Build quality is good. Plastic body build, feels like 100mm macro canon USM (NO IS). I would categorise this as Polycarbonate plastic like the one used in mobile phones/camcorders, with some extra support(mainly to the glass inside it). If I'd accidentally drop it on a soft surface(grass), I believe it would withstand the impact, but what will happen to the electronics inside...I don't want to know
If i'd drop it on gravel I see the plastic scratched, eventually cracked. The height of the fall is about 1.5-1.7 meters. Higher than this or a more solid surface => bye bye lens
The 18-55 kit lens would be more resistant to impact due to it's lighter weight and plastic/elastic construction.
However this is just an assumption for a worst case scenario. It really depends on the angle it falls, which part first hits the ground etc...
Focusing rings: As a Canon user, It doesn't really bother me that the focus ring is towards the body. I thought that it wouldn't be a problem having the zoom ring to "zoom in" by turning to the right, and "zooming out" the opposite way. I hear this is the Nikon way. However, I need to get used to it, it seems unnatural. If you ask me which way you need to turn the zoom ring on your canon lens? - I wouldn't know, but i guess i have this stored in my subconsciousness and it really can be bothersome with the Tamron.
The rubber used on the rings is a bit slippery(Maybe this is just my fingers). The focus ring could have been wider. The 88mm diameter of the filter thread is too wide for my hands(I suppose this is roughly the width of the lens barrel too). I have medium/normal sized hands, but i find stretching my fingers too much when zooming/focusing and it is a bit uncomfortable, but nothing to worry about that much.
Since the rings are a bit wide, if you are filming you cant perform a very smooth focus/zoom by hand.
The movement of the focus ring is ~90-95 degrees with medium resistance and the zoom ring movement is ~70 degrees with high resistance. It is good that you wont accidentally change the focal length(there is also a lock button), but bad when you do want to move the ring, because you don't know where the 24/70mm setting is since you need to apply more force, and you can be worried of applying too much force.
Fortunately the lens extends the proper way (Unlike Canon's 24-70) and everything seems to be tightly assembled.
All test shots are done with a 5dm2 with mirror lockup, iso 100, aperture mode, standard colour profile VC is off, manual focus in live view. I used a flimsy tripod, and the light conditions aren't perfect. I work at night, sleep late, and 5PM- 7PM is the only time I can do test shots. I live on the southern hemisphere it's winter here, so not enough light for the shots at f/4>( I will redo them). There Is some vibration due to the wind.
I think my lens is front focusing but i will get that fixed this weekend when i take some real life sample images.
For me, the colours of this lens are Superb, punchy & contrasty, and i love the bokeh no matter some people complain about it. I have tested the new 24-70 Canon m2, and the Tamron clearly performs better, with a more blurry bokeh. Some may disagree, i'm just having a say on my opinion.
I will just upload the images at f/2.8 and f/4 and will retake the others, since there is blur caused by shake, and the shutter speed at f/11 reaches 1/6 sec.
Feel free to comment the images. I do see wavy barrel distortion at 24mm and vignetting at all focal lengths.
There is no visible purple fringing.
I will keep you updated on focus speed and the rest. I need to get ready for work, and i still haven't even uploaded the sample images. Feel free to download them, all exif data is included....
... Now where do i upload them lol
Ok, I'm creating a Flikr account now.. BOOORRRIIINGGG
...Uploading 10 images.
I can't play Dota, because of the upload, and i really need that game it's my addiction
Whatever... I don't care if i'm late for work. Must play DOTA hahah
I'm having so much lag, 200> ms ping
All done http://www.flickr.com/photos/22285064@N03