Well, considering the price has been pretty stably above the current point (not stable in general but definitely above this point for months), I think it's safe to say if you had that Bitcoin you lost a potential opportunity to have made a lot more money. The worth is simply what people have been willing to buy at, and that price has recently been quite high.
I think it is safe to say people lost "a potential opportunity to have made a lot more money?" in 1000s of cases. Things are only ever worth what people are willing to pay for them. Just because that price has been high recently doesn't mean it's stable. Someone paid $4,500 for a Beanie Baby once.
So very true if you have to peg that 400mm to a specific exchange rate for another currency.
You can ascertain the value of 1 BTC in your favored currency rather easily given a choice of marketplaces. Less so with 100, or 10000+. Most market-places couldn't handle the volume without a substantial shift in price before your 400mm mark was hit for say, USD.
That said BTC seems to want to reach the type of ubiquity that allowed USD to be a universal currency of sorts during it's heyday. With means to convert in and out being varied from the strictly regulated to the strictly unregulated.