As a response to Facebook feeling more and more like a modern-day Yellow Pages, we’ve noticed (and written about) a growing number of exclusive online communities popping up. Ironically, two of Facebook’s first enemies, the Winklevoss twins, recently put down a cool $1M for funding one of these closed-door networks, SumZero. Judging by just how exclusive this network is, you’d think it was a country club application.

SumZero is a financial network that aims to capture an elite group of professional investors from private equity firms, hedge funds, and mutual funds. However, the criteria for admission is high (not to mention that Wall Street bankers and analysts are automatically out!). The network’s acceptance rate is about 25% so far, but once you’re in, you get access to the powerhouse community for $129 per month. So far, SumZero has a healthy network at around 7,500 members, but we’ll see if it can resist the temptation to expand.