I lived in the UK 13 years (and loved it immediately, when I moved there in 1998).
We moved back to my home country in May 2011. When I say 'we' moved back, I mean I moved back with my London-born DH and DC.
The first year was spent living in a city that even I didn't know very well. We didn't know anyone there. It was awful. A few months in we knew it wasn't for us and by a year in we had moved to a city I had lived in before (but wasn't my home city). We have been in city 2 for 19 months, but back here in my country for 2yrs, 8 months. Nearly 3 years.
We don't feel settled yet. The move to city 2 was definitely the right thing to do, and we are happier here. My best friend is here. We bought a house. DC1 starts school in a couple of weeks. But it has been hard, and I can't say we feel settled yet.
We had heard the two-year thing, and I agree with it. However, we did a year, and then had to start again, due to moving cities. So for us, it will be taking 3 years.
DH is very, very homesick. He misses his huge circle of old friends in London. It's impossible to replicate that.
He is giving it his all, though. But by the end of this year, if we're still not settled, then it will be decision time for us, I think.
And this was moving back to my home country, not even moving to a new place. I had just been away too long, I think. I'm very torn, and it will not be an easy decision to make.