The advantages are obvious.
.) In good lighting conditions, freehand no problem / If not, just something up ISO.
.) Lightweight - only 1190g
.) Integrated / Extendable sun shade
.) Minimum focusing distance 150cm - thus I use this lens very common for macro shots,
However, as with a tripod. (40D & 7D, when the 5D Mark II I mount the 1.4x Extender to)
The result is tack-sharp designs (insects & flowers) with beautiful bokeh at maximum aperture.
Otherwise, I use it when my 70-200mm f / 2.8 (without IS) is "short".
As disadvantage I could to something slow AF & evaluate the noisy IS - I did not do,
since it has no effect on the image quality.
Conclusion:
Have used it for over a year and would not miss it use - just great!