Google may be denying that there's a brain drain going on, as the BBC reports, but that doesn't mean it's not happening.

Really, what else could a Google spokesperson have done but denied there's an exodus? Google spokespeople practice public relations, not public humiliation.

This latest round of hand-wringing was prompted by the departure of Eliot Schrage, formerly Google's VP of global communications and public affairs, and now Facebook's VP of communications and public policy.

Schrage's exit comes only a short time after engineering VP Douglas Merrill left for EMI Music and VP of global online sales and operations Sheryl Sandberg jumped ship to become COO of Facebook. In addition, there have been other engineers moving to Facebook and to small startups.

Part of the reason this story has re-emerged is that it looks particularly bad when the head of global communications leaves. It's as if Schrage suddenly stopped believing in the message he had been delivering (though in all likelihood the move is about money and opportunity).

There is something to this "brain drain" thing, however. With stock options-vesting and Google becoming a mature corporate titan, those who crave the constant change and the crises of startups are naturally looking elsewhere for that adrenaline rush.

Bottom line -- it doesn't matter that much. There are plenty of brains at Google. It's not as if the entire engineering department or everyone with a PhD left en masse. Companies gain and lose people all the time.

The departure of a startup's CTO might mean the disappearance of necessary knowledge, but large companies can cope. Microsoft has lost a fair number of people to Google and its still standing. Apple has seen plenty of employees depart and -- last we checked -- it wasn't doing too badly either.

Talent ebbs and flows between Silicon Valley companies like the tide. Facebook will lose employees, too -- perhaps sooner than later if ads on social networking sites continue to underwhelm.

When Google's PageRank patent expires, that's the time to start worrying.