Ditto all of the above... you have to look at individual aircraft and see what's installed. Duncan and I have compared numbers on our 182s and they're different also, similar to his story about comparing with the A-model.
And... also have to be careful with the later models, those useful loads are based on MGTOW, NOT landing weight. If you want raw load carrying, as someone pointed out in another thread, the 235 beats the 182 because it's not an MGTOW weight, it's a max gross weight.
My 1975 Cessna 182 P-model, as it sits today... IFR /A equipped, with King avionics, ADF and antennas removed...
1/28/2011
Empty weight: 1815.9
Empty CG: 36.00"
New useful load: 1134.1
New moment: 65468.47
Max weight: 2950
80 gal @ 6 lbs/gal = 480
Full fuel useful load : 654.1
I can add an STC for $750 to raise the MGTOW to 3100 lbs, but MGTOW does you no good if you're not going to burn lots of gas. If you're going for raw load hauling, or need to tanker gas for IFR fuel minimums on short, heavy, hops... you won't get the full utilization out of it. It really helps you haul more FUEL, not "stuff" in the end. And don't land before you burn it off, or it's a mandatory inspection of the gear and aircraft.
You will however, have the widest CG envelope of any 182 built.
Not that it matters much, you'd pretty much have to be hauling 200 lbs (the maximum in the baggage area) of lead weights, and similar amounts of lead in the back seats with one tiny pilot up front, to get the thing out of the rear CG envelope. Fuel is virtually right on top of the center of CG, so even fuel burn matters very little in a 182.