When it comes to stocks, all growth streaks end. Sometimes, they end suddenly. (Just ask those who've been invested in Microsoft (NASDAQ:MSFT) or Intel (NASDAQ:INTC) for more than a few years.) But for Rule Breakers pick Akamai Technologies (NASDAQ:AKAM), the cash spigots remain turned on full blast.

Last night, the Web content delivery specialist reported even more Street-busting results. For the quarter, sales improved by 52% to $125.7 million, and per-share earnings grew 69% to $0.27 (non-GAAP). For all of 2006, sales were up 51% to $428.7 million, and per-stub earnings grew by 69% to $0.88 (also non-GAAP).

More importantly, management once again raised guidance. Executives predict between $1.26 and $1.30 in non-GAAP per-share earnings, on $610 million to $625 million in sales during 2007. As much as $30 million of the increase could come from recent acquisitions of Nine Systems and Netli, but even without these two, Akamai is projecting more for this year than it did in Q3.

As good as that is, though, higher earnings and even higher guidance are now expected.

How do I know? First there was the after-hours action. Akamai's stock bounced back and forth like a superball on concrete. Then there was this post from our Akamai discussion board. When Fools I respect begin to believe that beating top-line expectations by 3% is "a little weak," future disappointment is inevitable.

And that worries me. Akamai is a wonderful and, by all indications, enduring business. With a pristine balance sheet and a market-dominating service that commands premium pricing, there's no reason to not own this stock for decades -- except when expectations are so high that holding shares is like playing chicken with a freight train while driving a Pinto.

It may also be a bad idea to buy in when everyone has already bought. According to Capital IQ, institutions now own 83% of the stock. That's usually beyond my threshold for misunderstood multibaggers. Why? Blame Hewitt Heiserman, Jr., author of the excellent It's Earnings That Count. He once told me that when most funds already own a stock, their next decision is almost always to sell.

Conversely, when not enough supply meets panting demand, higher highs are inevitable. That's what happened with Akamai last year, and the stock more than doubled.

That can't continue forever, especially with so many frothy investors gobbling up the stock like it was Easter candy. Therefore, let this be your notice that I'm taking action. I'm not selling all my shares -- Akamai is too great a business for that -- but I am going to take some money off the table.

Today, Akamai composes roughly 10% of my portfolio. I think that's too much. So when disclosure rules allow, I'm going to trim my stake to roughly 5%, and invest the proceeds in another Rule Breaker. (You'll have to check out the latest issue of the newsletter to find out which one.)

Should you do the same? That's up to you. I won't blame you if you stick it out as is. With its latest guidance, Akamai is more than halfway to its 2010 goal of $1 billion in annual revenue. And there's no sign that its competitive advantage will fade anytime soon.

A web of related Foolishness awaits:

Akamai is a Motley Fool Rule Breakers pick. To discover all six of the stocks unearthed by David Gardner and his team of analysts that have more than doubled in the first two years of this market-beating service, try Rule Breakers free for 30 days.

Fool contributor Tim Beyers, ranked 1,640 out of more than 21,800 in our Motley Fool CAPS investor intelligence database, is a sucker for growth stocks and a regular contributor to Rule Breakers. Tim owns shares of Akamai. All of his portfolio holdings can be found at Tim's Fool profile. His thoughts on growth stocks, Foolishness, and investing in general may be found in his blog. Microsoft and Intel are Inside Value picks. The Motley Fool's disclosure policy is a rebel on Wall Street.