Thanks for the kind words, Sam. I was pleased with how several of the shots turned out. The practice should help for our Yellowstone trip, and we are planning another zoo visit before then (we bought an annual membership).
Carlo, if you are worried about weight, I've read decent reviews on the EF-S 55-250 lens. While it certainly doesn't compare to the 70-200 f/4 IS, it's quite inexpensive, small and light weight. If you do not think you will be using a telephoto much, it may suit your needs.
That being said, I would never get rid of my 70-200 f/4 IS. It's an incredible lens, and the size / weight do not bother me at all (it's smaller and lighter than my 100-400L). I use a telephoto quite a lot when we travel, though -- hence why I own both the 70-200 and 100-400. The 70-200's constant f/4 maximum aperture matches up very well with the excellent high ISO performance of the 7D, so you can use the combo in some lower light situations that used to require faster telephoto. I even used mine for some indoor ice hockey. The shot below was f/4, 1/1000sec and ISO 6400. I never could have done this with my old 40D -- I had to use my 85mm f/1.8 at the hockey games with that body.
