The IS is something that is very useful on the 70-200. Some people get headache but i find it very useful as it helps with my composition. When i want to shoot very tight, the optical IS helps me compose the picture so that i can get as tight as i want without accidently composing wrongly.
Also it makes photography easier even in bright condition. I know that as long as my camera is at 1/125 there is almost no way i can take a blurry photo (unless the subject is moving very very fast). I can be a bit more sloppy in taking pictures!!
Finally, with a TC, the IS lens becomes even more useful!!
Personally if you are not getting IS lens or the 70-200/4, get the sigma instead. There is a new version coming up with some macro feature (aka closer focusing distance). The sigma is a good deal because feature wise, it has everything (except white paint and a red stripe). Compared to buying a 70-200/4L with a tripod foot, the sigma is almost the same price!