I bought this lens to replace my kit lens on the 400d. Back then, I knew very little about the world of photography and i just wanted a good standard zoom. This did the job. NOTHING MORE.
If I could rewind time, I would get a 17-40L over this. For about 200 dollars more, you get a much richer tone and sharpness as well as a L-quality build.
After using this lens for a while, i realized that i use it as a prime at 17 usually. I've never actually captured any nice images at any magnification past 50mm.
Also, EF-S means its not compatible with the 5d FF-Sensor. If you want to stick with your 1.6 crop, this lens will do, but if you are planning to upgrade to a 5d, get the 17-40.
I recommend this lens to amateur photographers who just want a lens that covers decent range. If you plan on going professional, stick with the L glass, you almost cant go wrong.