I have the karachi outpost, which i personally love.
it looks nothing like a photobag on the outside, but can hold all of my larger SLR gear on the inside ( it fit 2 bodies, 6 lenses, and a 17" powerbook )
yes you have to take it off your back to open it up. but for me, i enjoy this extra safety measure. especially when i travel.
i also use a lowepro stealth AWII for light shooting days, it works very well for me. but i did have one instance where it wasnt zipped all the way and it fell open and dropped my camera straight to the pavement....
i have been contemplating getting one of their messenger type bags for my day to day use, but i've been hearing tales of woe about their longevity ?
at any rate, i love my backpack, its very comfortable, distributes the weight nicely, and holds everything i would like it to.