It'd be hard to draw a line on what's sketchy and what's not. Taxes are incredibly complicated. Defining what's legitimate business vs. ethically questionable vs. illegal (and whose laws are being violated) makes it hard to even categorize the money, even if there were data available on how much is there and who controls it.

My guess is that there's probably much more there that's completely legal, but pushes people's buttons because they want to see it taxed at home. Like Apple's overseas billions (which are largely sheltered elsewhere, but you get the idea).