Ok, I've got a Canon 18-200 IS, and also a 17-55 IS. I've been reading lots of threads about how great the 70-200 f4L IS is, and now I'm contemplating selling my 18-200 and saving up for the 70-200. For those of you who own or have owned the 18-200, have you thought about upgrading or have upgraded to one of the 70-200 lenses? If so, were you happy with your decision? I know I'll be losing the 18-70 range, but I have the 17-55 and am not to worried about the 55-70 range. Thoughts?
As for what I shoot, mostly outdoor family and friend stuff. I'm not a pro, though I aspire to be one day.
I have the 70-200mm f/4 IS as well, and it is excellent--I wouldn't consider the f/2.8 versions simply because they're too bulky and heavy.

