Great question. I'm surprised you haven't gotten any replies yet.
I can't speak to bilingualism personally, but I think Québec, Canada is a remarkably great example, particularly in Montréal. The province is officially French (with some fairly rigid language laws), the country is officially English and French, but the region is dominated on all sides by English.
People I've spoken to from Montréal could fool you into thinking they're American, I've always been impressed with their command of both languages, and although I've never asked specifically, I have to imagine they would tell you they're native in both. Frankly, if my goal was to master a second language to the level of a Quebecer, I'd be bitterly disappointed with my progress!