Our MUP's become unofficial off-leash parks in the winter, I guess because the drastic reduction in use during the "off-season" makes it more feasible. And I imagine it's a bit of a hassle to ski while holding a leash, too. When passing peds, dog or no, I find it's best just to slow down and be ready to stop as I roll by. Honestly, I think that I've more children wander into my path than dogs. But just try and suggest to the parents that they need to leash their kid; you better be ready to run or fight.
The only dog owners that bug me are the ones walking their dogs with really long leashes strung all the way across the trail, owners that don't pick up after their dog, and owners with aggressive dogs in public areas. Might be because I really like dogs, better than most people actually, because off leash dogs just don't bother me.