I really like my Kubota 500 too, it has hauled anything and everything I've piled into the bed, bags of cement or firewood,
I don't care what it's rated to haul/pull, I pile into the bed as needed and pull trailers as needed....... but, mostly I keep tools in it as I use it to get places on my property where I have work to do...
My brother has a Kawasaki Mule and a Kubota 900, I like my 500 better because it's narrower and goes down my trails much better/easier...
As for mud, it does pretty good, it's not like a higher powered model that you can slam through bad spots because of speed, but then again I can take that a step further and say that my Yamaha Grizzly 4 wheeler will go where the UTV's won't go too... But, for a work UTV, I'm very happy with my 500.
It's REALLY great that you and a passenger can easily slide into or out of it, my wife just LOVES it! And she'd rather walk than ride a 4 wheeler. lol
SR