Shorts get a bad rap. Any Internet message board that even lightly deals with the world of investing is almost certainly filled with banter blaming just about every bad tick of the tape on the folks with short positions. On a terrible day… it’s the naked shorts, of course.

It is a rare day that I will say anything negative about an investor that wants to lend shares today and pay for them tomorrow. Short selling is a vital, often extremely profitable investing strategy.

While few folks will admit it, shorts actually play a critical role in the markets constant search for equilibrium. They can even create profit opportunities.

That is certainly the case with NCI Building Systems (NYSE:NCS). Its shares are up by nearly 20% today on what would, at first, appear to be absolutely no reason.

But digging a little deeper, it is not hard to see what is likely

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Sirius XM Radio Inc. (SIRI) today announced a first-quarter loss of 7 cents per share, which was wider than the consensus estimate for a 3-cents loss.

Revenues for the provider of satellite radio service rose 5% to $605.5 million.

Meanwhile, the company boosted its full-year adjusted income guidance to more than $350 million, compared to earlier guidance of $300 million.

Analysts expect a loss of 12 cents per share for this year, but that has narrowed by 2 cents over the past 2 months.

Sirius XM, created by the merger of Sirius Satellite Radio and XM Satellite Radio, received a loan of $530 million earlier this year from Liberty Media Corp. to avoid a possible bankruptcy filing.

SIRI, a Zacks #3 Rank ("Hold") stock, has slipped more than 18% today on higher-than-usual volume of approximately 109 million, compared to average volume of about 64.7 million.

"SIRI" ...

By Mike Caggeso Associate Editor The dormant, yet important, proposed $5 billion merger of Sirius Satellite Radio Inc. (SIRI) and XM Satellite Radio Holdings Inc. (XMSR) cleared a major hurdle, as Federal Communication Commission Chairman Kevin Martin backed the merger - with stipulations. Concessions Martin recommended include: the stations turn over 24 channels to noncommercial and minority programming as well as a three-year freeze on prices and packages. Both satellite stations have already accepted Martin’s conditions. “As I’ve indicated before, this is an unusual situation,” Martin said in a statement. “I am recommending that with the voluntary commitments they (the companies) have offered, on balance, this transaction would be in the public interest.” Martin said Monday that he would propose the FCC approve of the conditional merger. Reuters reported that the proposal could be as early as this week, ...

In Monday’s Fast Money Web Extra, what M&A pair did the FM traders discuss?

In Monday’s Web Extra, Pete Najarian reveals which chip maker he thinks is a buy. Also the latest play on the XM / Sirius merger.

Disclosure: At time of publication, William Trent has no financial positions in XM Satellite Radio (XMSR) or Sirius Satellite Radio (SIRI).