Stocks declined today, with the Dow Jones Industrial Average (DJINDICES:^DJI) flat and the broader S&P 500 (SNPINDEX:^GSPC) down 0.7% and 0.5%, respectively.

The micro view: The wild ride for Green Mountain Coffee (NASDAQ:GMCR) investors continues, as shares leapt by nearly a quarter in after-hours trading today on the back of an earnings beat. In its fiscal fourth quarter, the company earned $0.64 per share on an adjusted basis (with Green Moutain, I would recommend investors make a particular effort to understand and track the accounting adjustments used to produce pro forma earnings), well ahead of the consensus estimate of $0.48 per share. The company also raised its guidance range for fiscal year 2013 earnings per share (EPS) from $2.55 to $2.65 to a new range of $2.64 to $2.74.

Even excluding today's after-hours action, Green Mountain shares have rebounded some 70% off their 52-week low, but they are still down roughly 60% compared with the 52-week high price. Momentum now appears to favor the longs again -- does that mean it's time to get into the shares? Not if you fancy yourself an old-fashioned investor rather than a stock trader. It's far from clear that Green Mountain may have established a competitive advantage early on with its single-serve beverage range, but whether that advantage is durable is another question entirely. As super-investor Warren Buffett told Fortune in 1999: "The key to investing is not assessing how much an industry is going to affect society, or how much it will grow, but rather determining the competitive advantage of any given company and, above all, the durability of that advantage."

Quite apart from any questions regarding Green Mountain's accounting, its advantage looks highly vulnerable to the attacks of a company like Starbucks (NASDAQ:SBUX) that has much greater resources and distribution and a well-established brand. In that light, I must consider that Green Mountain's shares are suitable only for purely speculative purposes. If you're looking for a comprehensive assessment of Green Mountain's risks and opportunities, click here to receive the Fool's premium report, which includes a full year of updates.

Alex Dumortier, CFA, has no positions in the stocks mentioned above; you can follow him on Twitter, @longrunreturns. The Motley Fool owns shares of Starbucks and has options on Starbucks. Motley Fool newsletter services recommend Green Mountain Coffee Roasters and Starbucks. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.