the sigma 15-30 is a great lens and i've never had any issues with it. i bought it a yr ago and it has it's own stylish carrying case. only problem is that the lens is rather large, but some people may prefer that.
it's a sharp lens, and after some tests hbr did w/ it, it proved to be very sharp stopped down to f/16.
basically every shot i've posted on my flickr page for the past few months and beyond has been taken with this lens.
i'm selling it cuz i recently purchased the tamron 17-50. i just needed a bit faster glass.