Carrying a dSLR while touring...
Sorry I'm late to this thread, but I've had the same problem for ages. I'm now at a Nikon D300, and if I have one of my big lens on, schleping this thing around my neck is a pain.
I took a cue from what I saw the brand Think Tank do. They have special "reporter" straps that basically clip the halfway points of the neckstrap to the shoulder straps of their backpacks. OpTech has something similar I believe.
So, I jury rigged something similar. It depends on what attachments, slots, etc. you have on your specific backpack shoulder straps and camera neckstrap. For example, halfway up my neckstrap (usually where the strap meets the softer material part), I threaded some "O" or keychain rings. Then, on my shoulder straps, I clipped on some small size carbiners. This way, I can clip/unclip the neck strap from the shoulder strap. Hint: always clip in first before you take off the neck strap, and always put the neck strap on first before you unclip!
This way, the neck strap is always there when you need it around your neck to move around quickly to take the shot, but at least you let the backpack weight counterbalance the weight of the camera during the inbetween walking bits, and it's resting on your much stronger shoulders and back, not your neck.
Not the most pretty solution, but arguably less "geeky" than a dedicated harness. Good luck if you give it a try.
(And yes, I have sling bags, etc., too, but when I travel, I want my bags to do double duty.)