Small, Fast and quiet
I have this lens on a Canon 450D body with battery grip and have found its size and weight well suited to this setup. I tried out the Tamron 18-270, Canon 18-200, Sigma 18-200 and older 18-250. To be quite honest didn't really have an issue with any of them regarding image quality and reach is actually fairly all similar. Didn't like the way the Tamron image jumps when using image stabilisation and the Canon is pretty big.
In the end I even bought this lens without trying it in the hope that it was similar is use to the Sigma 18-200 HSM as this was my choice prior to this one being released and I was not disappointed. The feel of the lens is very solid and has a very smooth action, similar to the Sigma 18-200. I tried out the older Sigma 18-250 and that had almost 2 levels of resistance depending on zoom length which this one certainly does not have.
The placement of the lens lock switch is excellent and I quickly got used to using it as its just so convenient even though lens creep is not a big issue.
You can really see the difference with OS on/off although I can't confirm how many F stops it really gives and don't really care as I can't change it now.
After using the lens for a couple of weeks I have sold my other lenses Canon USM 28-80, Canon USM 75-300, Tamron 1.4x & 2X teleconvertors and not having to change lens all the time is great.
As an all round lens its great and a real pleasure to use.
I can't really comment on image sharpness as I havn't done any real comparisons but will get around to it and let you know the result.
Also for $530 (In Australia) you just can't go wrong