US analyst outfit SharesPost has valued FarmVille creator Zynga at $5.51 billion.
According to the firm, its valuations are based on "recent transaction prices, current posts, research estimates and recent last round venture financing valuations".
SharesPost says it specialises in venture-backed private companies, using its various inputs to calculate prices and facilitates trades. To put the Zynga figure in perspective, it currently values Twitter at just under $3 billion and Facebook at nearly $33 billion.
Among gaming companies, Electronic Arts' current market cap is $5.22 billion, although the comparison isn't exactly fair given EA is publicly traded and Zynga's value above is based on a mixture of research and estimates.
What are other public games companies worth then? Well, Take-Two is a steal at $868m (unless you're John Riccitiello, in which case they won't let you steal it), and Activision Blizzard's market cap is a whopping $13.8 billion.
It's also worth noting that a company's market cap isn't necessarily the price at which you could buy the business - to do so you'd have to make an offer to the shareholders that was then accepted, and for that you'd expect to lump on a premium if the company was doing well.
In other words: MAGIC!