Friday was the first day of trading in public shares of social games publisher Zynga, following its long-awaited IPO. The company priced shares at $10, bringing in $1bn from the IPO and valuing the publisher at $10bn. So how did it do? Not amazingly, in that shares ended the day down on that initial price, at $9. Even so, a $9bn valuation for a company that was only launched a few years ago and which is almost entirely dependent on Facebook for its revenues is startling. The company has 54 million daily active users for its games, and in recent times has been signing marketing deals with major music artists: Lady Gaga and now Michael Buble.