A question for those who would have liked/would still like to emigrate: What do you think would be the best time, generally, for anyone to do it (regardless of circumstance)? Right after school/college? Or after some work experience? Younger or older? Single, married or with children?
Having jumped coast-to-coast intranationally and being familiar with the far-lesser challenges that poses, my instinct is that younger; right after school; and single are probably the easiest options. Here's why I think that:
1. You're likely to have fewer roots and community ties. If you're just coming out of school, then odds are high you've just spent some years living somewhere other than where you grew up/your hometown, anyway. You don't have ten years invested in a post-graduation hometown. It's easier to uproot things then otherwise.
2. If you're single, then you have fewer people's needs to consider. I've encountered many people on the East Coast and in the Midwest who have described moving to San Francisco as a lifelong dream - but one that is not feasible given the needs and desires of their spouse or partner and/or kids. This effect would probably be even clearer with an international move. For instance, my American law degree and bar admission would be much closer to useless in any other country, so if I had a SO who wanted to move internationally, I'd lean strongly towards saying no for that reason - it'd screw up, or at least greatly set back, my career. On the other hand, someone with transferrable work experience might have an easier time getting hired if they have more on their resume to offer a foreign company or institution. I bet this one's industry specific.
I could see how a young couple in agreement re: moving could have as easy a time as a single person...but there's still the possibility that the move could work really well for one person, and less well/not at all for the second person.
3. If you're young, single, and fairly footloose and fancy free, moving to a new place offers the possibility of building a new life, establishing your career, finding that significant other - and all in the place where you actually want to live. There's not the sensation of really having left a well-formed life behind somewhere. I think this is fairly important - at least it was to me. I was going to the place where I wanted to create my life. I think the same would hold true for an int'l move, but I think it'd be a bit more daunting. Fun, though!