They look like they would be fun for a short period, I honestly think their popularity is a fad, time will tell. For my uses they are completely impractical, not steet-legal, tiny payload, not up to par for self-supported travel. For a destination like Moab, looks killer, but then in Moab I would much rather be on my bike.
There are some serious concerns with any ATV subgroup including side by sides when it comes to land use and a sound outdoor/offroad ethic. Its not so much the user attitudes, rather its just so easy to go buy (or rent) and ATV and head to the hills with zero influence or education on proper etiquette. 4x4 users have the same issues albeit on a much smaller scale, and its a genera concensus that the anti-motorized cohorts have much less issues with street-legal full-sizes vehicles (such as a Jeep or pickup) than they do with "noisy", "out of control", "uninsured" ATV's. So many factors behind this influence obviously, legally allowing under-16 operators, etc.
The fact is the ATV community isn't 10% as organized as the 4x4 community, and the 4x4 community is only 10% as organized as they need to be. You do the math.
Total guestimate here, but if you were to survey 100 4x4 users at a random trailhead, my guess is 60 of them would be active to some degree with a club or forum (such as RME). 80 of them would at least be familiar with a different club or the U4WDA. The ATV users are seemingly far more disenfranchised, take the same number (100) of ATV users and my guess is that under 40 would even realize their are clubs in Utah for ATV's, likely less?
I'm by no means faulting the ATV associations or clubs, they do a great job when they can get an audience, much like U4WDA does a killer job given their budget, manpower and audience. Its just my belief that a 4x4 user is far more likely to get involved with a club or Association, the roster numbers are proof alone. Getting an audience is a huge issue, the 4x4 contention has a lot more opportunities. While there are quite a few ATV Jamboree type events throughout the state, as well as organized group rides, my guess is that they don't even hold a candle to the amount of 4x4 organized events. Moab for example has over 30 large 4x4 organized events, EJS, Land Cruiser specific, FJC specific, Cherokee, Grand Cherokee, Samurai, Nissan, Explorers, early Bronco, Blazer, etc, then think of all the club runs, all over the state. Again, far more opportunities that are still under utilized.