I had dilemma regarding f/2.8 IS II and f/4 IS (I wanted IS so f/4 without IS was not even a consideration) I am just into photography and learning a lot since last year with using 60D. I went ahead with f/4 IS since A) It's light in weight to carry when moving around with kids, B) It's light on my wallet to convince my wife and C) I am still learning, the most important point.
So I am glad I made the right decision to go with f/4 IS. Obviously with North East winters, haven't got a lot of good light to shoot, but this is a fantastic lens FWIW.