It looks like the expected Zynga IPO has appeared on the books in the form of an S-1 filing with the SEC. The filing is still subject to change (and incomplete as it contains a number of blanks) but it looks like Zynga intends to raise almost $1 billion from the IPO.

From the filing, Zynga mentions that they have an audience excess of 148 million monthly unique users in 166 countries who create and store more than 38,000 virtual items every second and spend 2 billion minutes a day with their service.

A bar chart shows their revenue from virtual items and online advertising rocketing up like corn growing in July from $36M in 2008 to $839M in 2010. They also mention in their brief that the social gaming company receives most of its revenue from a very small number of users and games.

“We rely on a small percentage of our players for nearly all our revenue,” writes Zynga. “A small number of games have generated a majority of our revenue, and we must continue to launch and enhance games that attract and retain a significant number of paying players in order to grow our revenue and sustain our competitive position.”

This isn’t entirely unexpected; most online companies with a multitude of products often have a trendsetter. They deal with this by branching out as much as possible and as often as possible.

The space holder of $1b may have come as a surprise to many industry analysts who predicted only $10m for Zynga’s IPO. As a result, it might reduce as the S-1 form gets filled in. Zynga did recently acquire mobile-games developer Area/Code and Newtoy. Only as of last February, their value found itself near $7b while seeking a new round of investment.

As Zynga’s IPO hardens and we know more about this, we do expect it to be a huge number.