Good idea: get that heavy DSLR off your neck. Many of us know the pain associated with a big ol’ camera and a four-pound L-series zoom. I avoid this by shooting with a Rebel and lightweight primes, but that’s not always an option.
Bad idea: hang your heavy DSLR off your hip, where your $1000 lens will constantly get bonked by your leg and whatever low obstacles you’re around. My 24-85mm zoom’s autofocus is unreliable now because of that kind of treatment. And the point of a neckstrap isn’t just to hang your camera around your neck, it’s also a safety precaution against dropping the thing — something the Spider Holster isn’t once you take it out of the holster.
My advice would be to get a good padded strap (not the one that came with your camera) and take the camera off your shoulders every once in a while — or use a lighter camera like a Rebel XSi. This solution is just too risky.