It’s a happy new year indeed for Mark Zuckerberg and everyone with financial ties to Facebook.  Goldman Sachs and Digital Sky Technologies have invested $500 million in the company, according to a new report, and in doing so, valued it at $50 billion.

A couple points of reference: it was only 38 months ago that Microsoft drew laughter by paying $240 million for a 1.2 percent stake in Facebook, valuing it at $15 billion.  And Yahoo and eBay just have market caps of about $21.7 billion and $36.3 billion, respectively.

This counts as a very significant milestone for Facebook, then.  Andrew Ross Sorkin and Evelyn M. Rusli, who first reported the development, noted, "The new money will give Facebook more firepower to steal away valuable employees, develop new products and possibly pursue acquisitions – all without being a publicly traded company."

Then here’s one other interesting detail: "As part of the deal, Goldman is expected to raise as much as $1.5 billion from investors for Facebook at the $50 billion valuation, people involved in the discussions said, speaking on the condition of anonymity because the transaction was not supposed to be made public until the fund-raising had been completed."

Anyway, although all this should ensure Facebook won’t run out of money anytime soon, it means Goldman Sachs is liable to handle Facebook’s IPO whenever the company goes public.

The hubbub, along with the plan to raise $1.5 billion more, may also mean the SEC’s rumored investigation into the trading of Facebook’s private market shares will become a little more serious.