Tamron AF 17-50mm F2.8 XR Di II LD Aspherical (IF) Nikon

I've had this lens for about 6 months. It's worked perfectly on my D7000 and I really enjoy using it. It's my normal walkaround lens, offering a great range on DX camera.

The good parts:
At f5 or above, it produces really sharp pictures, especially at f6/f7
It focuses quickly
It's manageable for weight and size, uses standard filters
It's REALLY good value

Not so good parts:
At 17mm it distorts
Colour depth is not quite right / not so intense as my prime lenses
At wide apertures, particularly 2.8, it is slightly soft
No M / AF clutch - you have to flick a switch to go manual

In mitigation:
Don't be put off by the minor negatives. I really like this lens and use it most of the time. The softness at 2.8 is manageable for pictures which you might otherwise miss because it offers such an aperture at such a decent price. At f4 and above it's sharp anyway.
The colour depth is sometimes slightly disappointing, but you can easily add a little in photoshop (or any other touch-up tool), and 'recover' your picture.
The distortion is only noticeable (to me) at 17mm, but can be fixed in photoshop if you're bothered. I usually don't go to the 17mm end if I'm photographing anything with straight lines, e.g. architecture.

Alternatives:
You're probably comparing this with 2 other lenses; the Tamron VC (vibration control) updated version of this lens, and the Nikon 17-55 2.8.
I've not tried the Tamron VC, but decided on the non-VC after reading various reviews which suggested the non-VC was optically better. Google search and you'll find the reviews from various respected sites.
I've tried the Nikon, and it was faster, slightly better wide open and had better depth of colour, but it is more than 3 times the price and weighs about 750g. SLIGHTLY better, but not £700 better.

In my view, you're better off with this non-VC Tamron, save the money vs the Nikon lens and use the spare cash to buy yourself the 50mm f1.8 and/or 35mm f1.8 from Nikon. The Tamron is a perfect walk-around, the prime lenses will do better than the Nikon 2.8 in low light. You can use the spare cash to buy photoshop if you don't already have something.

A cracking lens with some imperfections, but it won't stop you taking great pictures.

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A further update, several months later.
I stand by my review. Treat it as an f4 and you won't be disappointed, f2.8 is a little bit crummy, but f4 upwards is great.
I've added a couple of pics, check the user pictures. I tend to use this at 17-24mm range and it really shines, particularly at f5-f11.
I would now consider the Nikon 16-35 f4 vr as a competitor for this lens too. I've not tried this, but if you see yourself ever upgrading to full frame in the future, think about it. The Nikon 16-36 is expensive and heavy in comparison, and for a DX user the Tamron is a fantastic lens. I'm really happy, still.... You won't regret it.
I would consider giving this 5 stars and ignoring f2.8... just go to f4 and you'll be very happy.
Get yourself either/or the 35mm and 50mm Nikon for anything else! This lens is so cheap (for a lens, which is a very relative discussion!) that it's possible to get this and the prime lenses instead of the VERY expensive Nikon equivalent.

This is a legendary lens that delivers far better image quality than anything in the same price bracket though a similar spec Sigma optic is also very highly rated. The lens benefits from a constant f2.8 aperture and in all mounts it is available in has got rave reviews. Why? There is no manufacturer OEM lens that comes close to the amount of bang for your buck you get with this lens. I have found it to be sharp throughout the focal length range - in the centre at all apertures, and at the edges, reasonably sharp wide open and very sharp once stopped down a bit. Some reviews correctly note that field curvature reduces wide end edge sharpness a bit, but not too dramatically, and if you are very keen on edge sharpness wide open, e.g. for lanscape work, just stop the lens down to something like f7 or f8 and you get superb sharpness. The lens coatings give a pretty strong degree of contrast that reminds me of Zeiss lenses - very nice ! MEchanically and build wise this is good, but not quite up to pro lens standards like some of the pro Tokina lenses that built like a tank for example. Overall it's a great package - good focal length range, constant aperture and very sharp optics. Just watch out for some quality control problems as described by other reviwers here on Amazon.

the best lens at this range. it initially had some problems with the d200, but its a greate lens for cameras which relesed after the len released. for more info check the lab test of this lens, infact it is as good as the nikon premium range....