I read the reviews on this lense before buying it so I knew what I was getting into. Still, I'm very disappointed in it's performance in low light.
I bought this to have an all around lense for goofing around with, especially at family functions, holidays etc. What I found is that under natural light, I'm pretty satisfied with the quality of shots that it produces.
However, when using flash, it's terrible. No other way to describe it. I just shot several hundred shots at a Xmas gathering and about 50% of them are so soft, that they're unusable.
Will be returning it ASAP. Got it for a Xmas gift and am very unhappy with it. I have another Sigma zoom which I'm delighted with so I guess you get what you pay for with this lense.