Last week, social kingpin Facebook (Nasdaq: FB) saw the fateful expiration of its lockup period, setting loose over 270 million shares, free to find new homes, as their owners dumped them en masse. Shares fell 6% that day to fresh lows, only to briefly dip even lower --  below $19 -- on Monday.

Subsequent SEC Form 4 filings show that early investor Peter Thiel cashed out just over 20 million of his shares near an average of $20 per share, pocketing almost $400 million in the process. The sales took place between August 16 and 17 through various funds, limited partnerships, and LLCs that Thiel has a beneficial ownership interest in.

Thiel was an early Facebook investor, buying a 10% stake for just $500,000 as early as 2004, when Facebook was valued under $5 million. He also sold 16.8 million shares through Facebook’s IPO in May at the offering price of $38, bringing in $638 million. The latest sale unloads the majority of his remaining holdings, and brings his total haul from selling Facebook shares over the past few months to over $1 billion. He now owns less than 5.6 million shares, and has served on the board since 2005. Not a bad return over eight years if you ask me.

Of course, Netflix (Nasdaq: NFLX) CEO and Facebook director Reed Hastings recently bought some shares of his own accord, a week before the lockup. Hastings bought a little less than 48,000 shares at $21.03 for just over $1 million. That all sounds fine and dandy, but remember, that $1 million isn’t a large purchase for these bigwigs, especially in comparison to Thiel’s $400 million sale.

This unloading is less of a bearish sign for Facebook, but rather just a planned exit for an early investor ready to cash in his early investment. After all, going public is usually an exit strategy for many early venture capitalists who buy into startups in the early days. Thiel has also invested in other social media names, like Zynga (Nasdaq: ZNGA) and LinkedIn (Nasdaq: LNKD).

Instead of focusing on these insider traders, Facebook investors should turn their attention to the company’s monetization model, which continues to show improvement. Sponsored Stories is an important step in the right direction, and is off to a strong start. Grab yourself a copy of this premium report to read more on Facebook’s monetization challenges and opportunities. Sign up today and get free quarterly updates.