"More and more companies are using SecondMarket as an incentive tool," Aishwarya Iyer, public affairs manager for SecondMarket, told Betabeat. "We have CEOs who are telling their employees, 'We're doing this for you.'"

Seventy-six percent of the sellers in the private stock market were current employees, up from 60 percent in the second quarter, SecondMarket said in a release, and a dramatic reversal from previous years: former employees made up 90 percent of sellers in 2010 and 2011.

The continuing shift in the supply of shares wasn't the only change evident in SecondMarket's third quarter report: for the first time, the consumer web and social media category didn't rank first or second in total dollar volume, accounting for a scant 1.2 percent of transactions. In part, that may be a residual effect of Facebook departure initial public offering in the middle of the second quarter, but Ms. Iyer said the shift was also due to a more diverse mix of companies using SecondMarket to provide private liquidity.

What categories gained share? Consumer electronics dominated third-quarter trading, accounting for more than 75 percent dollar volume, with eCommerce responsible for another 19 percent.

Biotech and pharmaceutical companies may drive future sales. SecondMarket collects data on companies whose shares aren't available on the platform to gauge interest—there was $77 million in demand for the biotech and pharma category last quarter, with consumer web second at $45 million and software third at $43 million.

Meanwhile, SecondMarket highlighted companies that are attracting increased interest: potential buyers "watching" Meraki, the cloud-based network infrastructure firm, quadrupled in the third quarter, and interest in Codecademy more than tripled.

Can't get your IPO out the driveway.

The latest numbers don't bode well for those long suffering VCs hoping for an IPO exit. According to a poll from Thomson Reuters and the National Venture Capital Association, venture-backed IPO exits are at the weakest point, dollar wise, since the fourth quarter of 2009. In the third quarter of this year, only five such companies went public, down 77 percent from Q2 and 64 percent year over year.

That might be why New York magazine's lengthy Twitter profile reported, "The intense pressure to convert Twitter into a profitable business, and before a tech bubble pops, is palpable here."

But the bubble does come with another pressure valve.

The other preferred mode of exit, mergers and acquisitions, appears to be on the rise. "For the third quarter, 101 venture-backed M&A deals were reported, 35 which had an aggregate deal value of $6.3 billion, up 8% over the second quarter of 2011," reports MarketWatch.

"While the IPO market screeched to a halt in the second half of the 3rd quarter, the acquisitions market continued to move forward, said Mark Heesen, president of the NVCA. "Quality acquisitions continue to get done which should help venture capital firms return money to limited partners and better position themselves to raise new funds. However, current economic instability could reduce the number of high return acquisitions while keeping new IPOs at a seriously low level for the remainder of the year. Federal policymakers must address this market uncertainty if they want to fulfill the stated goal of increasing long term employment as it is these emerging growth companies that hold the key to future job creation in the United States."

And hey, VCs and founders in search of some liquidity these days always have the secondary market.