I understand and agree with many of the views here about how being a permanent, unrooted traveller can get a bit old after a while. In 2013, I took a little over a year off to go to China. I lived in a few different places around China for 3-5 months at a time, and did a variety of things - went to a language school for a bit, worked as an outdoor guide for a bit, did English tutoring for a bit, wrote news articles for an Asian-based website for a bit, and travelled around China and other parts of Asia for a bit. I was 26, and it was fantastic - my Chinese improved drastically, I met some great people, I had some wonderful experiences, and I grew a lot as a person. I think that going to China was one of the best decisions I ever made and don't regret it for a second.
I hadn't planned to go back home (to NZ), but I hadn't planned to stay in China, either. I was open to possibilities. When I did come home after 15 months abroad, I was so ready to do so. I missed cooking my own meals - even when I was living in a city, I knew it wouldn't be for that long so I never invested in much cookware and could pretty much only cook the simplest of meals. Living out of a backpack had gotten tiring - shortly after I returned to NZ, I purchased a soft toy/cushion thing and a large hairdryer and just relished the feeling of being able to buy things that were not essential but simply nice to have. I had also gotten sick of putting a lot of time and emotional investment into friendships/relationships only to know I would have to say goodbye soon (I am not naturally extroverted, and towards the latter part of my time there I put much less effort into making new friends). I gave up any hope of developing a serious long-term relationship. I had seen all my friends making progress in their careers, getting engaged, buying houses, etc and felt like I'd been stuck in a limbo. And I absolutely identify with what actionjackson said about doing something of more substance - for me, that was putting my hard-earned degree to use and developing my career. My first few months at my new (government) job after I got back were great - I was learning tons, and was getting great feedback on my work. I felt like I was making a useful contribution to society, and that people appreciated what I was doing. In terms of doing something "of substance" - in my field of law, it's difficult if not impossible to climb the ladder and gain meaningful work experience if you're always hopping around all over the place. There are some interesting internship-type opportunities but these are often unpaid or very poorly paid, so I wouldn't do more than one or two of them if I haven't FIRE'd yet.
That being said, I'm looking forward to going abroad again in the not-too-distant future after I FIRE in about 4-5 years. I'm now in a long-term serious relationship so hopefully that will ease some of the loneliness while abroad. I've given my career a decent go, have some good work experience, and find my current job frustrating. The plan after FIRE is to go to Portugal for 6 months, Thailand for 6 months, and then maybe settle down in Portugal for a while and do small trips around Europe, with a trip further overseas once every year or 2. Maybe after a few years in Portugal we'll decide to move elsewhere for a few years. Maybe we'll stay put in Portugal. Maybe we'll come back to NZ. Who knows? The world is such a large place, the possibilities are endless. But I also understand the downsides to long-term travel, and realise that I'll probably want some roots somewhere eventually.