Do the fixed-term contracts in academia lead to a brain drain?
I can only provide anecdotal data, I was going to  do this as a comment, but it got too big. 

I'm a postdoc (finished my phd in 2012), and I'm tired of it. In some cases (fapesp, brazil) postdocs don't have any rights or benefits (no vacations, for instance). 

Worrying about how I'll provide for my family from next August, when my contract ends, compromises my performance... More than that, I don't have continuity, I can't think of anything medium term, because I have no idea where I'll be in one year. 

I really like the projects I'm working on. But this whole thing has taken its toll on my and on my family. I'm seriously considering changing careers to get some kind of stability. I'd like to stay on research, but maybe research doesn't want to stay with me :)

update: I do not have kids, it is just me and my wife. We are postponing that exactly because I don't want to subject a kid to this. And its easier to move around when its only the two of us. If I'm honest, I don't know of any other non-religious profession that requires this kind of commitment. Maybe the military, but at least you got benefits, sometimes housing. And financial stability, if not geographical.