As recently as the end of 2006, most of us who watch big media companies closely were extolling the virtues of Comcast (NASDAQ:CMCSA). We were impressed with the breakneck pace at which the company was luring subscribers with its "triple play" offering of TV, high-speed data, and telephone service. Now it's almost the end of 2007, and the company has shed more than 35% of its price so far this year -- including a 12% haircut this week after lowering guidance. So what's the story here?

This year hasn't been as good to Comcast and its cable peers, including Time Warner Cable (NYSE:TWC) and Cablevision (NYSE:CVC). Economic softening has halted the previous brisk customer sign-up pace, while competition from telephone companies Verizon (NYSE:VZ) and AT&T (NYSE:T), along with satellite video providers DirecTV (NYSE:DTV) and EchoStar (NASDAQ:DISH), has intensified.

These conditions led Comcast to lower its guidance earlier this week. Comcast said its cable revenue would likely end the fiscal year up about 11%, rather than the 12% previously forecast. It also said its revenue-generating units (an RGU is one customer taking one service) would probably grow by about 6 million, rather than the 6.5 million predicted in its early guidance. The company also trimmed its cash flow and free cash flow expectations for the year, thanks to increased capital expenditure.

Sounds pretty bleak, if you ask me. But as if that weren't enough, Kevin Martin, head of the Federal Communications Commission, appears determined to ratchet up the regulation of cable in general and Comcast in particular.

Martin's efforts have involved an attempt to impose a so-called 70/70 rule to increase the FCC's oversight of the group. Beyond that, Martin is also pushing for the invocation of a 30% ceiling on the total share of viewers any one company can serve. That's just about the level that Comcast has reached, and so the rule would effectively stunt the company's further growth -- which is very bad news for investors.

In response to Martin's efforts, two U.S. House members introduced legislation that would shield the industry from increased regulation based on the 70/70 rule yesterday.

Add up all these crosscurrents, and the picture at Comcast -- which remains the best-managed company I've followed -- has become decidedly less rosy. There are enough hurdles in place that Fools should take a vacation from the company's shares.

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Fool contributor David Lee Smith spends far too much time examining the product of his cable providers. He doesn't own shares in any of the companies mentioned. He welcomes your questions or comments. The Fool has a disclosure policy.