Groupon (GRPN), the Chicago-based daily deals company, began trading publicly today. The company's $12.7 billion initial market value is the second highest valuation in tech history. The first place spot is held by Google (GOOG), which had a valuation of $23.1 billion on its first day of trading in 2004.

So exactly how long can Groupon sustain growth?

It may be dependent on the new products Groupon has been releasing — not the daily deal emails that the site is known for.

According to YipIt, a daily deals aggregation site that also tracks data collected from daily deals websites, Groupon's local business deals gross billings, or the amount customers have been billed, has declined from $367 million in the second quarter of 2011 to $358 million in the third quarter of 2011 — about a three percent fall.

This decline in gross billings is important because Groupon makes a percentage of each sale hosted on its website. When gross billings decline, so does revenue. According to data provided by YipIt, Groupon's newest products have been driving overall billings growth.

Groupon Getaways, Groupon Live and Groupon Goods have done particularly well among all divisions in the company. The three groups were able to generate $36 million of billings, which made up nine percent of the total North American billings.

The data highlights a shift in the Groupon business model. During its roadshow, while Groupon was trying to generate interest among investors, the company was marketing itself as a local e-commerce marketplace rather than a daily deals company.

In the online roadshow, Groupon described its new product Groupon Now! as Groupon 2.0, indicating a radical shift in the company's strategy. Groupon Now!, which was released in May, is a location-based deal offers program that plots deals onto a map. Consumers can view Groupon Now! on a computer or on a mobile device.  According to slides from the company's roadshow, Groupon predicts that mobile deals will represent 50 percent of Groupon's sales within the next two years.

While Groupon touts the viability of Groupon Now!, YipIt has been tracking data from the service and notes that it's off to a slow start. According to YipIt data, Groupon Now! was only able to generate $1 million in billings across 25 markets during September. The amount was less than one percent of the company's gross billings on the month.

The slow growth of Groupon Now! isn't because of a lack of marketing, either: it's currently being promoted through a $10 credit given to anyone that uses the new platform. It's also being promoted in Groupon's daily deals emails. Still, Groupon Now! has not expanded to a new location for more than three months. The slow growth of Groupon 2.0 is not a good sign for the long-term growth of the company, which, according to the online roadshow, is contingent to the growth of the company's new platform.

The most crucial point from YipIt's analysis is the distinction between two different business models at play: Their point is that Groupon's local business deals — their original and still most prolific source of revenue — is a push business model, meaning that the company contacts subscribers and tries to get them to purchase goods. Groupon Now! is called a pull model because it aims to get users to open an application or website that allows them to view nearby deals. The traditional platform contacts the consumer. The new platform needs consumers to contact, or view, it.

The distinction is important for two reasons: Not only are these two services entirely different in terms of their relationship with the end-consumer, but there is also a large discrepancy between the billings that each platform has able to generate.

In essence, the platform that Groupon is touting as the future of the company isn't generating cash, and Groupon's traditional method of making cash is dwindling. Another important data point from YipIt shows that quarterly revenue growth has dropped 101 percent from the fourth quarter of 2010 to the third quarter of 2011.

All these points — the drop in Groupon's quarterly revenue growth, the slumping daily deals billings and the radical shift in the company's strategy — indicate that Groupon's dramatic entrance into the public market is ripe for short-selling.

Technology companies, notably Amazon and LinkedIn, have been targets for short-sellers who bet that the outsized valuations and skyward growth prospects are set too high. Short sales are executed when an investor borrows stock and sells it in the hope that it can be bought at a cheaper price. The net outcome is a profit.

Bloomberg Businessweek reported that after the initial pop of an IPO, the jump from the initial offering price to the open, 20 of the 25 hottest IPOs in 2010 and 2011 dropped significantly. The report notes that the 25 hot IPOs slipped 31 percent on average from their opening price. Many slipped more than 50 percent. The 333 IPOs that Bloomberg has data for slipped 11.1 percent. The difference between hot IPOS and all IPOs is 38.9 percent.

The future of Groupon remains largely undetermined, and, in many ways, has just begun. As the company tries to grow its new pull business model, it will evidently face several challenges. The company will likely succeed for years to come, but for the 5 percent of the company that is floating in the public market, it's fair to say that, unless people begin using Groupon Now! soon, the share prices have a high probability of dropping significantly.