The premium-cable channel is obviously feeling its oats, as buzzworthy original series like Californication, Dexter, and Weeds have led a 2 million jump in subscribers, to 16 million, over the past two years.

Some analysts agree that Showtime, as a stand-alone stock, could be the secret weapon of CBS shareholders. On its own, "Showtime would probably be worth more than CBS today," says Porter Bibb, a managing partner at Mediatech Capital Partners in New York.

"It's hot, it has an interesting future, and it's making money with video on demand."

Of course, not every premium pay-TV channel would perform as well as a stock. HBO, for instance, is probably better served—for now—by remaining a part of Time Warner, under intense pressure as it is to deliver hot, game-changing new shows with the frequency it used to, says Bibb.

But in general, if a media property is strong, it performs better outside of a conglomerate than inside one. Why keep a company's most valuable assets hidden inside a decaying shell?

The Dolan family's Cablevision, which owns a slew of valuable cable networks through Rainbow Media—including the Sundance channel, IFC, and AMC, home to the breakout hit Mad Men—is another example of a media company whose stock is undervalued.

Cablevision would do well to spin off some subsidiaries—or even just stop making new acquisitions. After paying almost $650 million for the paper Newsday, the company got very little back in terms of stock value.

G.E., which has been urged to spin off NBCU by eager analysts, no longer has that luxury with G.E. Capital suffering in the economic crisis. But should it do so in the future, the new company—made up of a movie studio and theme parks, with business models that are not advertising-reliant, plus a mature slate of cable networks with dual revenue streams—would likely perform well in the stock market.

News Corp. and Disney are two possible exceptions to the big-media curse. Disney makes sure that ESPN programming on ABC, for example, is obviously marked as such, an effective cross-marketing tool. And News Corp. is steadily integrating Dow Jones' components, such as MarketWatch, into its daily operations.

But even the most skilled managers are overextended when trying to grapple with the various subsidies of their enormous conglomerates.

A(nother) case in point: YouTube has lost some of its tech-darling status since being swallowed up by Google. Perhaps that explains the new partnership with CBS, which aims to expand YouTube's niche from clips of cats falling from trees to more mainstream content like you'd find on Hulu.com. But can one mammoth media company save another?

"I don't believe in conglomerates from a financial point of view because they totally depend on having good management," says Bibb. "That's a tough thing to depend on."

In other words, don't count on it.