I'd suggest actually handling the f2.8 version of the 70-200 before making your decision. It's a fairly large beast, and while the size and weight don't bother some people, they did bother me. Like you, I'm an enthusiastic amateur and take my camera everywhere. I used to own the f2.8 non-IS, and found I was leaving it at home more often than not, simply because I didn't want to carry it. I found it to be an encumbrance, for example on trips to the zoo or the park with my daughter, when we had other stuff to carry around. I eventually sold it, bought the f4 IS instead, and couldn't be happier. The f4 IS is significantly smaller and lighter, and I carry it everywhere. It produces outstanding images. For general use, don't underestimate the usefulness of IS on a lens in this range. My keeper rate, even in low light, is much higher with the f4 IS than it was with the f2.8 non-IS.
Bottom line, the f4 IS is a very versatile piece of equipment that does a superb job in most circumstances.