$39 billion.

That’s how much investors have collectively lost on Groupon , Pandora , Zynga and Facebook since those companies went public. It’s the kind of performance that can almost make you nostalgic for the good old dot-com days, when the fleecing of mom and pop investors was left to the Pets.com and iVillages of the world.

Just consider some sorry stats.

Since their IPOs, Pandora, Groupon and Zynga have lost a respective 41%, 66%, 68%. Even Facebook, the most anticipated IPO since Google , is off some 26% since its May debut. The combined earnings of those companies over the past twelve months reported? $226 million.