The long-awaited initial public offering for Zynga is reality — but as some investors celebrate, others wonder whether the numbers being discussed in conjunction with the company are a sign that we’re in the middle of another Internet stock bubble.

Zynga, the maker of massively popular Facebook games like FarmVille and Mafia Wars, filed for an IPO Friday and said it plans to raise $1 billion — – a figure that is expected to go higher by the time its shares begin trading.

A final IPO figure is likely to emerge in the next three to four months as bankers determine the offering price and how many shares should be sold. If high-end estimates prove true, Zynga could emerge with a valuation that’s bigger than any publisher in the video game industry.

A high valuation would come with a notably higher multiple. Gaming giant Activision has a 6X multiple, Take-Two and Ubisoft have 8X multiples and Electronic Arts comes in at 11X — all within acceptable limits for most investors.

Zynga, if it sticks with the $1 billion mentioned in the S-1 filing, will have a $10 billion valuation, giving it a multiple of 19X. If it bumps that IPO filing to $2 billion, the valuation jumps to $20 billion and the multiple soars to 46X, which some may consider high.

The 1990s Internet bubble was caused, in part, by investors and venture capitalists pouring money into companies that were never profitable — or even close. That’s not the case with Zynga. In its S-1 filing, the company reports 2010 profits of $90.6 million, with revenue hitting $597.5 million. In the first three months of 2011, it has earned $11.8 million on sales of $235.4 million.

At the end of the first quarter, Zynga games averaged 62 million daily active users. Collectively, those players spend 2 billion minutes per day interacting with the games. And the number of people playing them has increased steadily since September.

While most users of FarmVille and Zynga’s other games only play the free portions, the company said it relies on a “small percentage of players for nearly all of our revenue.” Those players pay small amounts of money for virtual items in Zynga games. It did not break out what percent of players pay.

Zynga relies on its partnership with Facebook to succeed. Zynga, in its S-1, said it makes “substantially all of [its] revenue and players through Facebook and expects to continue to do so for the foreseeable future.”

To protect future earnings, the company has been diversifying. A year ago, Google invested $100 million in the company — and many expect Zynga games to be a large part of the emerging Google Plus social network.

The company also makes money from in-game advertising.

Zynga’s rise has given many in the vidgame industry cause for concern, especially given how much time players spend with the games.

Wall St. analysts, though, say those worries are likely overstated.

“We do not see Zynga’s business as cannibalizing the packaged goods business, at least for hard core games,” said Michael Pachter of Wedbush Securities. “We think that Zynga has captured some of the ‘Guitar Hero’ and ‘Wii Fit’ crowd — primarily women — and expect the company to continue to grow the games category beyond the traditional 13-30-year-old male demographic.

“However, we do not think that Zynga’s success spells doom or failure for the traditional publishers, as we are confident that the hard core gamer is here to stay.”

The filing could benefit rival Electronic Arts. one of the few companies that has invested in social network games with its Playfish acquisition in 2009. EA shares spiked last week when talk of Zynga’s filing began to circulate — and climbed 2.5% Friday.

Disney, meanwhile, is focused on social games, but because the mouse house is divested in so many industries, Zynga’s filing isn’t expected to ping the radar of its investors.

CEO Mark Pincus founded Zynga in 2007. It employs roughly 2,300 people, mostly in San Francisco. Morgan Stanley and Goldman Sachs are leading the offering’s underwriters.