I received a bag this week, the lowepro's pro messenger 200. After trying 3 other bags (slingshot 302aw, event messenger 150 and flipside 400; all lowepro's), I think I may have found the perfect bag for me. I will still use my flipside for the long walking distances, but this one seems to be an excellent all-purpose bag.
Really love it; you can put a lot of stuff in there and the bag's extra padded strap makes it easy to carry around. Not made for long walks tho, but you can have everything handy and swap lens in seconds. I can store my D800 with lens attached, 3 more lenses (14-24, 24-70, 70-200 and 50mm), flash, teleconverter, Ipad and spare batteries and still have room left for an extra body and a lot of knick knacks.
The gf's starting to hate tho... 4 bags and I cant get rid of any; they all seem to have their respective usage.