Some other fund managers are more specific, offering either an exact price or relatively narrow price range. All of them, however, charge fees. This typically includes both a management fee and a carried interest. It's kind of like investing in a venture capital fund -- or even a traditional direct secondary fund -- except for the lack of transparency surrounding portfolio company financials.

    So why pay 2-and-20 (fees of 2% of assets and 20% of profits), or some variation, to a fund manager who is more of a middleman than someone who performs due diligence? Basically because such deals can be prohibitively expensive for retail investors to do solo.

    For example, say I had $250,000 that I wanted to invest in Zynga. I could go to SharesPost or better-known rival SecondMarket, and hope to find a seller match. But then there would be legal fees and other closing costs. Plus, Zynga would probably charge me a few grand to approve the share transfer. In other words, the bad bargain from a firm like Felix may be better than no bargain at all.

A sustainable market?

    Investors and fund managers interviewed for this story agreed that more and more of these funds will continue to be formed and funded. What seems more uncertain, however, is whether such a niche market can be sustained.

    Most of the big funds being raised are focused on just a small handful of companies: Facebook, LinkedIn and Zynga. Expect that Twitter will soon join that rarified air, but it's currently a difficult company to trade on the secondary market (Sacca is one of several people who has a special agreement with Twitter management, perhaps because he's a company advisor and was an early investor off of his own balance sheet).

    Each of those companies -- with the exception of Twitter -- would probably have gone public in most any other era. Maybe the financial meltdown got in the way, or perhaps there are simply a few too many iconoclasts like Mark Zuckerberg in the mix. Either way, it's not inconceivable that each one will have completed an IPO by this time next year.

    If so, what will firms like Felix look to acquire? For that matter, what do the secondary exchanges trade? Is there another group of multi-billion dollar start-ups that retail investors will buy without even a cursory look under the hood?

    My guess is no. This is a special purpose time. But that's okay for retail investors. After all, they can always buy shares on the Nasdaq.