Billionaires and their closest allies recently launched a full-court press against California's proposed wealth tax, which would levy a one-time 5% tax on billionaires' net worth. Google co-founder Sergey Brin, now worth nearly $300 billion, likens the tax to Soviet oppression and has spent roughly $57 million to oppose it. He and a few fellow billionaires are even threatening fleeing the state to avoid it.