How hot is social networking? Investors will find out in a few months when Classmates Media, a pure-play social networking firm goes public.

The company, which runs the Classmates.com Web site, filed for an initial public offering Monday evening. Classmates.com, which allows people to reconnect with old high school and college friends, is a dot-com survivor. It’s been around since 1995 and has more than 50 million registered users.

Since 2004, it has been a subsidiary of the publicly traded Internet access firm United Online (UNTD), which owns NetZero. United Online investors seemed to like the IPO news. Shares gained about 8 percent in mid-morning trading Tuesday.

Like most social networking firms, Classmates is growing rapidly. Classmates reported in its registration filing with the SEC that revenues surged 64.3 percent in 2006, to $139.4 million. And in the first quarter of this year, sales soared 68.6 percent, hitting $42.4 million.

This is important to note because when I wrote late last week about how very few dot-coms are seeking to go public these days, people told me that due to regulatory compliance issues, it only made sense for a company with annual revenues of over $100 million to consider an IPO because of how costly it is to be a public company in the age of Sarbanes-Oxley. So size is not going to be a problem for Classmates.

It is also not throwing its eggs in one basket from a sales standpoint. Classmates generates revenue both from advertising and subscriptions. The company also owns online rewards site MyPoints.

What’s more, the company has impressive investment bankers behind it, with Goldman Sachs, JP Morgan and Deutsche Bank Securities listed as its underwriters. Classmates is hoping to raise $125 million in the offering. The company plans to trade on the Nasdaq under the ticker symbol CLAS.

So can Classmates be the next Google (GOOG), or for that matter, the next VMWare (VMW), the virtualization software maker that surged more than 80 percent out of the gate in its market debut Tuesday?

Classmates has an impressive track record but it has some things going against it that could keep it from being a blockbuster IPO.

For one, although Classmates may meet the requisite revenue requirement for a public company these days, it falls short in another key metric: profitability. Classmates reported a net loss of $1.9 million in 2006 and another net loss of $250,000 in the first quarter of this year.

But Ali Mogharabi, an analyst with B. Riley & Co. who follows United Online, points out that Classmates is generating positive earnings before interest, taxes, depreciation and amortization, or EBITDA. This measure of profitability, often viewed as a proxy for how much cash a company is generating, is widely used by media analysts and investors as an important metric for valuing a company.

Classmates reported EBITDA of $23.2 million in 2006 and $5.1 million in the first quarter of 2007. Mogharabi, who doesn’t own United Online stock and whose firm does not have a banking relationship with United, said he thinks a fair value for Classmates once it starts trading is about $600 million, or 12 times his 2007 EBITDA estimate of around $50 million.

But Classmates also faces a lot of tough competition in the social networking world, including from several larger public companies. The company lists in its IPO filing that it considers News Corp.’s (NWS) MySpace, Yahoo (YHOO), Microsoft’s (MSN) and AOL, which, like this Web site, is owned by Time Warner (TWX).

MySpace, in particular, is doing extremely well. When News Corp. reported its fiscal fourth quarter results last week, the company said MySpace is on track to generate $800 million in annual revenue in fiscal 2008, which ends next June, and that the Fox Interactive Media unit that owns MySpace should post operating profit margins north of 20 percent.

Several of Classmates’ privately held competitors are also going to be formidable threats, including the ultra-hot Facebook, LinkedIn and Reunion.com. What’s more, they would arguably be better investments if they went public.

LinkedIn, which has talked about possibly going public in the next year or two, also is growing rapidly. Plus, it has said that it is profitable. Reunion.com, which received a $25 million round of venture capital financing in April from Oak Investment Partners, said at the time of that funding announcement that it too was profitable and that revenues were doubling annually.

And then there’s Facebook. Given all the buzz — and traffic — it has generated since it opened up its site to developers of outside applications, it stands to reason that if any social networking firm had a chance of having a healthy IPO, it would be Facebook.

Nonetheless, Classmates is going to beat its rivals to the public markets. And for what it’s worth, Classmates does generate a lot of traffic. According to the most recent figures from Web tracking firm comScore Media Metrix, Classmates had 13.9 million in unique visitors in July.

Classmates trails MySpace and Facebook but it did have more visitors than Reunion.com, LinkedIn and Military.com, a site owned by Monster Worldwide (MNST) that focuses on keeping members of the armed forces connected. Classmates also lists Military.com as a competitor in its IPO filing.

Still, one venture capitalist said he’s not sure that Classmates will be a huge hit with investors or advertisers since the site is geared more toward getting people reacquainted and is not necessarily as “sticky” as other social networking sites.

“I’m not sure Classmates is like a Facebook, MySpace or Bebo,” said Jeremy Liew, a partner with Lightspeed Venture Partners, a VC firm that has invested in popular widget company RockYou and Flixster, a social networking site focusing on movies. “Classmates is primarily about getting back in touch with people rather than staying in touch. People are using Classmates more like a classic directory and not for ongoing communication. So there is a massive difference in page views per visitor and other forms of engagement.”

So how the stock does will be an important test case for the scores of other social networking firms out there. As I pointed out last week, most social networking companies seem content to stay out of the public markets for now. And if Classmates gets Wall Street’s version of a dunce cap, then nothing is likely to change.

But if Classmates gets an A from investors, other social networking companies will probably try to test the public waters as well.