I would suggest that 90% of people who have fewer than two children and don't regularly haul construction materials, straw or the like would do better with an xtracycle than with a trailer. I am glad trailers are out there, in all their variety; I'm also glad I can hitch them to my xtra.

Also, there's a category of jobs for which an xtracycle is the clear winner, namely hauling long loads such as 8 and 12 foot lumber, kayaks, and surfboards; adults tend to be a drag to carry in a trailer, also. I can picture myself, with a couple reinforcing straps, carrying two fifty-pound bags of dog food on either side and two fifty-pound bags of concrete on the top, which is the rated capacity of the xtracycle. If one has a trim road bike, turning it into an xtracycle is either a drag or impossible, while hitching a trailer is likely to still be straightforward; not everyone is going to want a long bike all the time, even though most of us turn into raving fanatics about ours once we have them up and running.

If it gets you hauling your personal freight by bike instead of by motor, it's awesome.