First of all I apologize for the desk lamp behind the camera, not it is not some contraption holding the flash
I just purchased this lens, though it was not the lens that I originally wanted, that being a 28-70mm EX DG lens, not DG Macro. Sigma markets this as being a macro because, I am assuming, of the close focusing range of the lens, that being about or just a little over 12 inches at all focal lengths.
The lens is quite heavy but not overly so, it gives one the feel of having something hanging off the front of the camera. Zoom is 180 from Canons design. Fully extended the lens is at 24mm while retracted its 70mm. For some that may not be useful but for me, I kind of like that since I seldom shoot wide angle but it is nice to have that capability if and when I want to.
I have read some horror stories and some words of praise over this lens. The reviews on B & H Photo are mixed and for the most part I take them as the writers are being extremely picky, comparing the lens to Canons L"s or have little experience with such lenses to reasonably comment on them and then there are some who may have just gotten a bad lens period. It happens. If you are one of those who compares everything to a Canon L lens then don't buy this lens.
But if you want a lens for all round use this seems to be it. Not a true macro but really a good "close-up" lens in my opinion, you can always enlarge the image in PS or Photo Impact and say that it is a macro. One other thing that most catalogs and web sites seldom show is the lens extended. In this last photo I have shown just that. The lens is "extended" to its 24mm setting, making it over all about 7 1/2" in total length with the "included perfect lens hood." Filter size is 82mm. The lens overall seems to be very well built, not a lot of wobble in the front element when extended, unlike the Canon 28-135mm which wobbles and bobbles when extended to 135mm, though it is still a good lens but prone to dust. At present the Sigma seems to be tight in that area and the zoom and focus are quite smooth, though not fluid in movement it still is easy to operate. The lens can be used in manual mode while in AF and the AF is very quick and quiet, though others may have commented on it being quite noisey, I beg to differ at the moment. There are two settings or switches though for auto and manual focus. One is at the base of the lens, like Canons, while the other is at the focusing ring. By gently sliding the focusing ring forwards, it positively locks the lens in the manual focusing mode, there is as far as I can tell at present, no problem of it sliding back into AF mode but to use this lens in the manual focus mode this feature must be employed. Overall a great lens at present, though only time will tell but I like it! 
The flash works very well up close and the intensity of the flash can be controlled in both manual and ETTL modes of operation. As for the cameras operational mode, I always shoot in the manual mode of operation. "Auto everything," IMO, is the worst thing that anyone could have done to any SLR, digital or film I think. It takes the "thinking" out of photography.