I've bought this fix lens to complete my new 5D's package....
I've hesitated between this lens and the best-seller 17-40L, but as I've a fisheye Zenitar 16mm and a nice zoom beginning at 28mm, its range has appeared to be ideal.
The most important : its incredible sharpness on full format cameras like my 5D, with very moderate distorsions.
Very useful for architecture or seashore landscapes... And its lightness allows you to keep it always in your camera's bag. Its small filter size (58mm) is very useful to exchange filters with other lens like Canon 501.4 or 100mm2.8Macro.
I bought it at second hand, 200 Euros so the third of a 17/40L.
I think this lens is under-rated because of its medium performances on APS sensors cameras, but on a FF like 5D it's a gem !