I drove my X across the country and can attest to it being very capable on road. It is a comfortable ride, not a lot of road noise, plenty of space for hauling my stuff, and has a great sounds system with the iPod connection.
I was in the car about 12-13 hours a day and was only mentally tired, not physically tired from driving. I can't say that for the Jeep I used to own back in college where it felt like I was in a fight after 3-4 hours on the road. Not really a surprise, but the only drawback I had was encountering high winds which tend to blow the truck around. As long as you expect to have that it is no big deal.
Xterras really are great road trip vehicles. Just the right size for 2 people and lots of stuff.
