I got an op-up NRT-JFK in 2004 as Gold, and NGO-ORD? NGO-JFK? last year as PLT. Only did one international leg on American this year and for that I did the 25K miles/$250 upgrade each way on JFK-NRT.

I've been at the top tier on Delta since 2001; I'm batting 5/8 on op-ups JFK-VCE in the last three years (lots of tourists buying coach seats), and maybe 1/10 on op-ups on other international legs. As others have said, you can't count on it but it's nice when it happens. I would suspect that all airlines, when faced with an oversold-in-coach situation, would first seek to bump up their elites, and then would go down the list in frequent flyer categories. Certainly that seems to be what Delta will do, though once I saw a late-checking-in non-elite also getting the op-up on VCE-JFK because all coach seats were already assigned.