|Lets face it: how many budget zooms are out there which let you take decently sharp zoomed in pictures?
This lens is a very good alternative to the otherwise expensive (but amazingly performing) white beasts from Canon (yes I am talking about the Canon 70-200mm L series). I owned it for about 10 days, only to return it. Not to say that I did not have fun with it, but I had to work very hard with it to get what I had bought it for: good zoomed in views of birds etc.
This lens has its limitations in terms of chromatic aberrations (noticeable more at high contrasty edges), softness beyond 200mm or so (and I really mean softness due to the optics and not camera/lens shake because I tested with a tripod and timed shutter release etc.), slightly faded warmer colors, etc. But it is still very good if you want to start experimenting with mid-tele zoom lenses.
Its actually not a bad lens for beginners. In fact I would highly recommend this lens for beginners, so they can work it out without image stabilization and solid built and high quality optics.. it really made me appreciate how much old school guys worked to get decent zoom images without all the IS and VR gadgeted lenses.
Good luck, and happy imaging!
Review: Sigma 70-300mm f/4-5.6 DG APO Macro Telephoto Zoom Lens