I only use the Canon supplied case to store the lens at home when I am not using it. When out shooting I have been using a Tamrac UltraPro 7, a messenger style bag designed for a DSLR and two lenses plus accessories. It has room for my 24-105mm f/4 L plus the 70-200 along with my 5D2, and I can also squeeze a 1.4x III TC and a 25mm extension tube in there without things getting too crowded. This setup gives me a lot of flexibility for basic travel photography with minimal bulk and weight. (I have a bigger bag for more serious photographic trips.)
I like the messenger style; it is compact for the capacity offered and it doesn't look that much like a typical camera bag so it attracts less attention. I also find it keeps the weight closer to the body, which limits shoulder and back strain (helpful with the 70-200, which is a bit of a beast). The Tamrac also has a rear pocket which unzips and becomes a sleeve, allowing it to slide down over the handle of roll-aboard luggage. This works great for air travel!
The only thing I am not sure about is whether the 5D2 will still fit if I add a grip, something I want to do soon. I am finding it awkward to shoot in the vertical orientation with the 70-200 or the 300 f/4 L, especially with the TC attached. Is the grip too big for bags of this design?
BTW, I took a peek at the Lens Exchange design on the Lowepro website, and I love the concept! I can see this being very handy for travel also.