OK so getting close to committing to new lenses but just like some input.
basically I'd like to get a 70-200 IS either the f2.8 or the f4...
Now I seriously like the idea of the f2.8 model and can live with the price but a number of on line test such as http://www.photozone.de/8Reviews/lenses/canon_70200_28is/index.htm and several posters on Fred Miranda's review site have voiced some issues with "bad copies" being noticeably worse (without even resorting to pixel peeping) than the f4 version.
Also most of the reviews tend to reenforce the idea that the 70-200 f 4 L lens is one of the best zooms as far as image quality goes.
I can live with the loss of a stop as my current telephoto zooms are the 70-300 f4-5.6 IS and the Sigma 50-500 f4-6.3 so at worst I'm not losing anything aperture wise over what I've already got but hopefully gaining sharpness and contrast.
Also I'm hoping that with in the next year I'll also upgrade my camera from my current 20D to a 1D MkIII which has about 2 stops gain in ISO quality - looking at test shots I took with both cameras in low light the noise at 3200 on the 1D MK III is almost as low as the 20D at 800. As such it's a case of what I lose on the swings (getting the f4 version) I'll more than make up for on the roundabouts (the 1D MkIII)
Also with the lower cost of the f4 that would leave more than enough change to allow me to get a new wide angle such as the 17-40 f4 (my current wide angle is the cropped image circle/asp digital sensor Sigma 10-20 which would not work too well with the d1 MkIII (I'd be expect some serious vignetting on that) plus it's "OK to fair sharpness" wouldn't do justice to the 1D Mk III.
Though I do mostly shoot in good light I'd still like to be able to shoot in environments such as these:
http://www.pbase.com/marxz/yoiyama
http://www.pbase.com/marxz/sanjoohashi
note the noise/iso difference between the first and the second gallery is due to upgrading my D60 to a 20D in the week between the two shoots - that gained me an easy whole 1.5 to 2 stops of usable ISO.