I just got this lens and i'm glad i saved up for this. i previously had a 200mm f2.8 L prime, and i really liked that one, but with a 1.6CF body it wasn't really suitable for me. i shoot mostly portraits, and the 200mm is a little long for portraits. After reading the numerous good reviews here i decided to take the plunge and get this one.
i've only owned it for a few days, but right off the top, the sharpness and contrast is much better than my 70-200mm f4 L at 135mm.
it's smaller and lighter than most of the L zooms, and is only a little bigger than my 17-40L.
Bokeh is really in a class of its own. i'd say its as good as the 200mm L prime, if not better. i've never seen or used the 200mm f1.8, so i can't compare or comment.
i think i'm going to keep this lens for a long time. i've already got the 35mm f2, 50mm f1.4, 85mm f1.8, the 135mm f2, the 70-200L, 17-40L and a few other less mentionable canon EF lenses. of the lot, my favorites are the 50 f1.4, the 135 f2 and the 70-200L.
lens hood is big. i know it's big because it has to be, but storing the lens in my bag with the lens hood really takes up so much space. overall the lens is amazing enough for me to live with the size of the hood.