Tamron's got some great lenses. Their 17-50mm f2.8 is also a very nice lens. However they do have some issues with consistancy of quality, and many people have reported new lenses off-focusing front or back, and have had to go a few rounds with Tamron's tech to get it resolved. They don't charge, other than shipping, though, so even if they don't get it right the first time eventually they will. It's just something to add to the consideration.
However, the Tamron 28-75 f2.8 is one of the lightest and smallest mid range zooms around, and the image quality of a good copy is very good. It's a stellar walk around lens for light duty use, I wouldn't recommend it for someone who needs a rugged lens that could take a few knocks, but for general use, I'd agree, it's a fantastic deal.