Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of session border control specialist Acme Packet (Nasdaq: APKT) soared as much as 21% in intraday trading after the company reported fourth-quarter earnings results.

So what: Acme Packet clobbered expectations; it's as simple as that. Revenue estimates were $60.8 million for the fourth quarter and Acme reported $70.2 million, which represented a 70% increase over the fourth quarter of 2009. Non-GAAP earnings per share also outpaced Wall Street's view, clocking in at $0.26 per share versus expectations of $0.23. As if that wasn't enough, the company boosted its 2011 outlook from the guidance it provided back in October. Previous revenue guidance of roughly $287 million was jacked up to $300 million while non-GAAP earnings per share were raised from $1.00 to $1.05.

Now what: I have a tendency to gripe about tech companies that still like to pretend that stock-based compensation doesn't exist, and so the fact that the primary difference between Acme's GAAP and non-GAAP results is the impact of stock comp gets my goat a bit. Particularly notable is the fact that while 2011 guidance for non-GAAP earnings per share was increased, the guidance for GAAP EPS actually fell from $0.78 to $0.76.

A bigger consideration for investors, however, is the stock's current valuation. Trading at 63 times the non-GAAP EPS guidance for 2011, Acme shares look darn expensive. But the company has been growing like a weed and may still have a big runway ahead of it. So what investors need to be chewing on right now is just how big the Acme Packet opportunity is and whether the company can continue to grow at a rate that will justify that kind of valuation.

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Acme Packet is a Motley Fool Rule Breakers pick. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.                                                          

Fool contributor Matt Koppenheffer does not own shares of any of the companies mentioned. You can check out what Matt is keeping an eye on by visiting his CAPS portfolio, or you can follow Matt on Twitter @KoppTheFool or on his RSS feed. The Fool's disclosure policy prefers dividends over a sharp stick in the eye.