I currently have a Tamrac slingshot bag, the Velocity 9 and it holds a fair amount of stuff.
Currently I use it with my Pentax Spotmatic with a 100mm f4 macro lens mounted. In addition I also carry the 50mm f1.4 prime, 28mm f3.5, 200mm f4 and the 300mm f4.
The Spotmatic is about the same size as the 20D if that gives you a relative comparison. I placed it on the counter at my local camera shop since I thought the newer cameras were so much bigger and heavier. And here I thought the Spotmatic was relatively small. Well, compared to a 1DSMKII it is, but then so is a MiniCooper.
I also generally carry about 10 rolls of film, assorted filters, cable releases and other stuff including a lightmeter.
The bag is reasonably portable with the strap across my chest and is not too uncomfortable. It also has a waist strap that I have not used and a grip/handle on the top when I just want to carry it without having it on my shoulder. I can access most of what I need while carrying the bag across my shoulder. Since I am right-handed, the bag sits on my left hip, but it also works the other way too for those of you who are left-handed.
The shop did not have the similar model from LowenPro at the time I bought the Tamrax, so I could not make a direct comparison, but I am satisfied with my purchase.
From what I have seen in the VJ, Michael carries everything in the back of the SUV he travels in and uses a vest when out of the car.