Or make sure you know how to use it, because an AWFUL lot of the shallow DOF "problem lenses" appear to actually be user error.
Don't actually own one, my comment was just based on professional reviews I'd read when considering getting one. I did get a Sigma 24-60 a while back. I think it was about 3 weeks before the AF crapped out and I had to pay shipping to send it in for repair. No problem with the other 2 Sigmas I use though (17-70 and 10-20), but that was pretty annoying.