Picked it up used in mint condition. Paid a bit too much, but came from a reputable local camera shop with a 90 day warranty. I'm very impressed with the optics, true bargain optically. A tad soft wide open, but still useable and miles better that what Canon offers in it's price range. I had been using a Canon 28-105 USM f3.5-4.5 and found the Sigma to be miles ahead in sharpness at all focal lengths/aperatures.
But the focus motor is a real dissapointment. It's slow and noisy. My lens motor started to get stuck so I took it in for service and found that it basically would cost as much as I paid to replace the motor. Argh! I took it apart myself and lubricated the brass motor gears (it's a very old fashioned mechanical design) and it seemed to solve the issues.
It's a love hate thing. I just love how the photos from it come out. They're stunningly crisp and contrasty for a low range zoom. If you don't mind taking time to pose your shots then this is an optical wonder. It's dissapointing if you try to use it for action sports. It's just too slow. Canon USM is dreamy in comparison. It doesn't support manual while auto focus is on. You need the SG version.
Lens hood (comes with) is a better design than Canons. Sturdy and secure and take bashing about very well.
Would I buy it again. Definitely. It has some limitations, but wow, what an optical stunners. The proof is in the results, I have hundreds of great shots from it.