I have the 70-200 F/4 L and it is a very nice lens - very sharp, great colour, nice zoom range, comfortable size to hold (for me), tripod collar & lens hood included, works well with my Tamron 2x adaptor and Kenko extention tubes.
However I wouldn't recommend it if it's the only lens you can afford or want to carry around.
My second lens is the 17-40 F/4 L, which is also excellent, but not as good as the 70-200, as it shows some edge distortion particularly at open f-stops (but probably not a fair comparison considering the focal lengths).
Both are excellent lenses but each one requires the other to complete the zoom range, which means you get stuck with 2 lenses. If I only want to take one lens I take the 17-40 and it usually works out fine, especially for normal happy snap stuff.
I'm not sure what's available at the moment, but if there is something that goes in the range 17 - 150 or 200 at good quality that is the lens I would consider.
Regarding IS, I think it's worth every cent. My partner has a 100-400 F/5.6 L which I often use, it has IS. I can take 400mm shots with it at 1/30th OK and 200mm shots at 1/30th second no problem at all, where as with my non-IS 70-200 I need to be around 1/60th or preferably 1/120th to completely avoid shake problems. And the 100-400 is a 2kg lens, so hard to hold steady sometimes, especially after carrying it around all day hiking!
I often consider selling the 70-200 F/4 L and buying the new 70-200 F/4L IS, just to have IS. But it'd still cost me a few hundred, which is hard to spend
Enjoy the shopping, it's fun looking for a new lens
