It is a truth universally acknowledged, in the business world at least, that if you can afford a $100 million home, you're doing something right. Russian venture capitalist Yuri Milner has done a lot of things right, namely founding Mail.ru Group, the largest Internet company in the Russian-speaking world, and then putting his money behind U.S. up-and-comers Zynga, Facebook, and Groupon. Last January, Milner entered into a joint venture with SV Angel called Start Fund; the partners agreed to invest $150,000 in every new Y Combinator startup, without necessarily knowing what the company does. The deal gives Milner access to a stream of new ideas for a very modest investment. If the fledgling entrepreneurs need incubator space, perhaps they could set up camp in Milner's new 25,500-square-foot Silicon Valley mansion, believed to be one of the most expensive American homes ever.