The quote below is from an article re: the loss of wealth from technologists on the Forbes billionaires list.
Facebook’s Mark Zuckerbergdidn’t make the list this year, however, with his estimated net worth dropping from $1.5 billion to $600 million. He’s still smiling though.
via techcrunch.com
My last attempt to value Facebook put them close to $6 billion so I guess by that standard, Mark owns about 10% of Facebook. However, if you're taking the valuation from the ConnectU lawsuit, it's $3.7 billion making Mark's stake a little over 16%. I'll assume Forbes is using the publicly available number and not mine ;-)