I have 2 systems. My leica and 28mm f2 I carry in a Billingham L2, in the winter I sometimes just carry it in my coat pocket. My D700 with 24mm f1.4 I carry in a generic backpack. I prefer that no-one knows I am carrying a camera.
When travelling on an aircraft or long distance bus, I cram both systems into a Billingham bag which is also large enough to take my 17"mbp and accessories (charger, HDDs etc). I wrap the cameras in a sweater or hoodie, or similar to prevent damage.
The problem I find with "camera" bags is that they look just like a camera bag, this applies to both the over shoulder type and backpacks. Living in Sao Paulo, it really is better to be more discreet.