Will the current march of IPOs ever slow down? If the first-day pops of last week's new issues are any indication, probably not. Three firms debuted on the market over that span and all experienced first-day stock price advances. The three -- Splunk (Nasdaq: SPLK), Proofpoint (Nasdaq: PFPT), and Infoblox (NYSE: BLOX) -- are fast-growing but unprofitable tech companies. Despite their red ink, they flared on their respective debuts, portending good times ahead for new stocks. But not all IPOs are created equal.

It's the revenue, stupid
For new issues of recent vintage, revenue is king. The first-day share price pops of the three firms corresponded directly to their most recent annual revenue growth. Splunk's was a juicy 83% while Infoblox and Proofpoint grew at relatively modest rates of 30% and 26%, respectively. The share prices of the trifecta rose a respective 109%, 33%, and 8% on their market debuts.

None of the three have made a dime lately -- or ever -- but does it matter? Investors are willing to accept the often-inherent unprofitability of young tech companies as long as their sales advance significantly. All of the three musketeers continue to add to that top line, although Splunk is maintaining a higher and (so far) steadier pace of growth than its peers.

What also helps is that these companies actually have solid underpinnings to their business. They count among their client lists Bank of America, Viacom (Splunk), Adobe Systems, Caterpillar (Infoblox), and the federal government (Proofpoint).

Time will tell if they're able to keep these big spenders as customers. All three operate in hot tech areas that, now or in the future, will attract determined competition. Splunk is a data aggregator and compiler that has been described as a "Google for machine data" -- "machine" meaning any modern computing device. Infoblox, meanwhile, integrates a client's hardware and software in order to automate and simplify computer networks, and Proofpoint concentrates on solutions for corporate security and network protection.

Accentuate the positive
If recent IPO history is any guide, it's the companies with at least some small competitive advantage or a scrap of profit that maintain or grow their first-day share price jumps. Although its long-term viability could be questioned, LinkedIn (NYSE: LNKD) has posted a few small but positive net profit numbers here and there. Optimistic investors really like this, and the stock now stands a mighty 133% above its issue price.

In my opinion, Yelp's (NYSE: YELP) business model seems unimpressive when stacked against many Internet peers, but the company has incredible brand recognition for customers seeking reviews of local enterprises. As such, it still trades high, up more than 50% of its day-one launch.

This is a discriminating market, though. Groupon made a splashy debut but its share price has been eroded by sharply increased competition and accounting mistakes, among other problems. The company's stock has declined by nearly 50% since its debut. Similarly, licensing costs are putting the hurt on Internet radio broadcaster Pandora Media, whose shares have also degraded by about half.

Splunk, Infoblox, and Proofpoint are all young companies that will, in all likelihood, continue to lose money in the near future. In the meantime, the trick will be to hold on to their key clients, carve out and defend or grow meaningful market share... anything to keep the market thinking positively about their prospects.

Some investors will keep their eyes on the IPO space -- and pounce on any firm that has even slightly positive fundamentals. There can be little doubt that in the coming months we'll see more issue day price explosions that will continue to defy gravity. However, long-term investors need to be selective and evaluate a company's sustainable competitive advantages. A team of Motley Fool analysts identified a rapidly growing company that has delivered exceptional returns year after year in our special report, "The Motley Fool's Top Stock for 2012." The growth story is far from over, however, so download your copy now.