Well, I do have awesome calves, glutes, and thighs! ;D
And it does burn fat all over. Even in the midsection. I've found that having "6-pack abs" tends to reduce my overall stamina though. A little additional body fat goes a long way in overall performance for me.
Shoulders get a good workout too, but not so much on my arms for some reason. Even on a good hardpack singletrack. Maybe my fork is doing some of the work my arms should be doing.
