Mr. Market seemed to forget about Linux vendor Red Hat (NYSE: RHT) for a couple of months. The stock had gained 47% over the previous six months, leaving it unmoved by a perfectly respectable earnings report, as a lot of good news had already been priced in.

Since the third-quarter report, Red Hat got swept up in whatever currents and eddies course through the high-growth portion of the market, rising when fellow growth phenoms (NYSE: CRM) and VMware (NYSE: VMW) rose and falling as they swooned, with no significant bad news or analyst downgrades to drive Red Hat's own chart squiggles.

All of that nonsense came to an abrupt halt yesterday. Red Hat's fourth quarter caused blunt trauma to the average analyst's expectations (poor guy), with $0.26 of non-GAAP earnings per share on $245 million in revenue. The resulting 18% pop erased those three months of negative action. CEO Jim Whitehurst will tell you that Red Hat has only just begun to nibble at a truly massive market, jam-packed with low-hanging fruit.

In an exclusive phone interview with the Fool, Whitehurst said that open-source software such as Red Hat's core products is coming into its own after decades of proprietary software hegemony. Led by devout open-source users and frequent source code contributors including "the Googles (Nasdaq: GOOG), the Facebooks, the Zyngas, and the Twitters" of the business world, new-wave corporations are showing that you can get real business done with open, low-cost software. That influence is now "bleeding its way into the enterprise," Whitehurst posits.

The enterprise software and infrastructure markets that Red Hat is attacking add up to somewhere between a $50 billion and $100 billion annual sales opportunity, depending on how you define market boundaries -- and assuming that you're buying high-priced solutions from incumbents Microsoft (Nasdaq: MSFT), Oracle (Nasdaq: ORCL), IBM (NYSE: IBM), and other sticker-shock artists.

That's about the size of the market opportunity that lies ahead of Red Hat, which is about to break the $1 billion annual sales benchmark in the coming year. Even if you account for a cost-to-own difference where Red Hat is, in Whitehurst's words, "nearly an order of magnitude lower cost relative to our competitors," it's still easy to see Red Hat growing like the dollar weeds in my yard as the company starts grabbing serious market share.

Make sure you don't miss it when Red Hat takes off -- just add the stock to your Foolish watchlist.