There is absolutely no problem using D800 as a walk around camera

FWIW, I used to carry a Nikon F3 on an MD-4, a bunch of lenses, and the occasional Hasselblad and its accessories when I used to shoot in college and on vacations. Yes, my back and shoulders got achy at times, but the images were worth it.

Today I was shooting my kids' lacrosse games with an NEX-7 and its 55-210, and while it was certainly lighter, it's not the D800 that's arriving on Monday. The Sony has its place, but so does the Nikon. I think the DSLR isn't dead yet, and I plan to walk around with the new Nikon too.
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david