It's always interesting to see what billionaire investors are doing with their money. Sure, you can't match their gains simply by copying every single one of their stock picks, but it can still be helpful to know what they've been up to.Consider that the billionaires, hedge funds and big-time advisories listed below have a great deal at stake. And their resources for research, as well as their intimate connections to insiders and others, can give them unique insight into their stock picks.Study