Investors will soon be able to snag -- or pass -- on Groupon.

The wildly popular deal maker is going public, filing its prospectus yesterday with the SEC.

Outside of Facebook and perhaps Twitter, Groupon is the most anticipated dot-com IPO. This makes last month's debut by white-collar social networking site LinkedIn (NYSE: LNKD) seem like an appetizer.

It's too soon to begin talking about valuations, though it will be in the tens of billions. Underwriters and the first wave of public buyers will be the ones that decide exactly what price tag Groupon fetches in the coming weeks. However, we now have our first true glimpse under Groupon's hood, and the engine may surprise you.

Top-line growth is there in droves. Groupon moved $713.4 million of its pre-paid vouchers last year, and revenue soared to $644.7 million during just the first three months of the year.

The heady growth isn't a surprise, but let's go over a few things in the prospectus that may throw you for a loop.

1. Groupon is losing a lot of money
All along we've assumed that Groupon has a license to print money. It sells discounted city-specific experiences, pocketing as much as half of that before passing on the rest to its merchants.

Margins have to be huge, right? The reason that niche-specific leaders The Knot (Nasdaq: KNOT), Travelzoo (Nasdaq: TZOO), and OpenTable (Nasdaq: OPEN) announced similar initiatives last year is because this is presumably where chunky net profits like to party.

Well, not so fast.

Groupon posted a loss of $456.3 million last year. Nearly half of that was acquisition related, but the red ink continues to flow with a whopping $146.5 million deficit during this year's freshman quarter.

This doesn't mean the model is broken. It's actually just the price of breakneck expansion, as Groupon is now available in 175 North American markets and 43 countries. A much smaller Groupon posted a net loss of $6.9 million in 2009, and that was largely the result of preferred stock dividends.

2. Groupon isn't as greedy as you might think
Groupon's popularity is based on a simple win-win-win scenario.

Restaurants, spas, and any area merchants with the flexibility to offer a deeply discounted experience in exchange for a wave of customers flock to Groupon and smaller copycats. Deals are generally half off, giving customers a great price break. Groupon typically requests to keep half of the proceeds. When a deal is small -- say $4 for $8 worth of drinks at a local bar -- Groupon may even ask to keep all of the money.

Well, reality paints a different picture.

The amount that Groupon reports as revenue is the full amount of the prepaid deals. To find out how much it keeps, investors need to go two line items lower to arrive at gross profit. Last year, Groupon kept just 39% of the revenue generated from its daily deals, though that did spike up to 42% during the first three months of 2011.

In a nutshell, Groupon isn't always splitting things 50/50, so prepare to haggle, merchants.

3. Groupon engagement isn't so great
There were 83.1 million subscribers to Groupon's daily deals, but we're not talking about tens of millions of bargain seekers popping down offers as if they were daily vitamins. Groupon sold just 28.1 million offers during this year's first quarter (and if you're a glutton for data, divide the quarterly revenue of $644.7 million into 28.1 million to arrive at an average deal price of nearly $23).

This doesn't seem like a very engaged audience, but there's a statistic that's even more shocking. Only 15.8 million of Groupon's 83.1 million registrants have actually purchased a deal through the site.

Don't get me wrong. Having 15.8 million cumulative customers for a company that wasn't even around three years ago is phenomenal. This is the reason why the big boys are moving in. Google (Nasdaq: GOOG), (Nasdaq: AMZN), and Facebook have all dived in recently.

However, the illusion of Groupon appears to be more valuable than the reality.

Marketing costs alone last year were nearly enough to swallow down its entire gross profit. Going from competing against cash-strapped upstarts to well-heeled giants may force gross margins to contract.

The growth is there, but this isn't the slam-dunk that many fans and investors were hoping they would be getting. 

Will you be a buyer of Groupon after it goes public? Share your thoughts in the comment box below.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.