I use a Sigma SD14 and purchased the 18-200mm DC OS lens for that camera to use on vacations for snapshots or when I don't want to lug a bag around for a day of shooting. After getting a Canon 7D, I wanted the same "solution" even though I have a good collection of lenses for it. My choices were down to the Sigma 18-250mm DC OS HSM or the Tamron 18-270mm Di II VC. Since that Sigma has HSM which the Tamron lacks, and I've had nothing but good experiences with Sigma lenses, I opted for the Sigma. I have not regretted my decision. This lens has met and even exceeded my expectations. Build quality is good, the lens is solid but not too heavy which is how a DC lens should be. The AF is fast, the HSM works well. The zoom is well-damped and the focus ring is also.
If anyone expects stellar performance from a superzoom like this, they'll be disappointed but no one should have that expectation. This is a good lens that produces good shots, some are quite sharp and color rendition is spot-on. Any lens with this zoom range is going to be a compromise. Knowing that, my epxectations have been met or exceeded by this lens. For anyone looking for a all-in-one solution when the circumstances merit, this is a fine choice.