It's an excellent performer in the real world and a cheap alternative to the far more expensive and heavier 28-70/2.8 AFS lens. Optically the lens has low barrel distortion and light falloff in the corners and gives really good images between about f5.6 and 11. The lens has 15 elements in 12 groups and takes 62mm filters. Weight is quite good at 655 grams (compared to 935gr for the AFS 28-70). It's available in AFn and AFn-D versions.
The examples I've used have quite noticable flare when shooting near the sun in harsh lighting conditions.
My only bitch with the lens is the rotating front end of the lens that makes using a polarizing filter a bit of a pain, but this is a minor drawback given the quality of the lens and it's low price on the used market.
Used prices range from about 250 to 400 USD depending on version and condition.
It's a far more capable performer than the Sigma and is better than the highly rated Tokina. Build quality is excellent.
I've had this lens for over 8 years now and I'm still using it. What I really like about it is that it is a true zoom... you can focus on a subject at 70mm and when you zoom out to 35mm, the subject is still in sharp focus. Most zoom requires you to re-focus.
One known problem with this lens though is that because it is a push-pull zoom, there is the zoom creep issue. When you zoom out to 35mm and tilt you camera/lens up, the barrel will slowly creep back down to the 70mm position. This is only a major problem if you are taking picture on an inclined plane... but for this to really to be an issue, you'd be having your system mounted on a tripod. Otherwise, you left hand would normally be holding on to the lens!