My parents have two Polaris 2-up Sportman 550s (forgot the exact model name) and there's few things more fun for 4 people, even if all 4 have no riding experience of any sort (common sense notwithstanding). I've really been surprised a few times at how much gnar they can handle...they are hill-climb beasts and feel so sporty for a utility ATV platform and one that is slightly enlarged. I'd say they can go about as fast or faster than I ride on my KLR650 in all conditions except open dirt. The only problem is the passengers (2-up) can really get thrown around when going faster and it can be tiring for them. Otherwise they are outstanding vehicles that have done everything asked of them and more and have been the utmost representation of reliability and durability.
We tend to ride all day or for a weekend at a time while camping, riding as much as 100 miles a day which seems like a lot when its mostly dirt bike trails on vehicles designed for relatively slow cross country travel. I tend to ride them most during the winter when the snow makes riding 2-wheels impractical. Riding them during the winter is when it's really an adventure! Where we go, the area is closed to full-size vehicles during the winter so it's by-and-large empty and itching to be adventured on. While it really gives me the itch to ride 2-wheels during the winter when I can't for weeks at a time, it's a welcome alternative that also allows me to bring friends a riding experiences when they are otherwise incapable, uninterested, or fearful of joining me on bikes.