i have one in the sony KM alpha mount, currently can only use manual mode as the af mechanism is damaged due to an accidental drop., its AF is noisy no doubt and hunts so much in low light condition but if used outdoor with good light, is very fast. am considering sending to sigma just waiting for their e-mail reply, if not will probably use this in manual mode forever..
The 70-300mm F4-5.6 APO DG Macro is a good lens if you know how to use it well. The one I used to own was a Nikon mount non-motorized version, AF was snappy under good ambient lighting and IQ is good. Never had any problems with it before. I'm not sure about your version though, since Sigma has released the same lens with motorized AF.
I have been using this lens few months back, mainly for shooting birds. IT is not ideal but I don't want to fork out a lot of money only to realise I am not that interested anymore. Ok. Here are my observations.
Build wise it is not bad. Quite comfy to handle. Its auto-focus is good, doesn't hunt in evening light conditions. Night time depending on subject it may hunt, but this is the same for many othe lens so not an issue.
It has no IS and the effect is obvious. It shows up. Or maybe it is my hands or skills that is shaky. Anyway most will advise you to use a tripod if you are using at 300mm for wildlife. Do that and it should be fine. I have my miss shots but my better shots are really pretty good (for the price of this lens)
As a side note, the macro function is not a real macro one only 200-300mm can activate and I heard the ratio is 1:2 instead of 1:1 in ideal macro lens.