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

Today, the stock market once again failed to gain traction, extending its losses so far in 2014 in giving up what had been a solid advance early in the day. Somewhat sluggish readings on the services sector of the U.S. economy raised some concerns about the health of the overall economy's expansion, but that didn't hold back Pandora Media (NYSE:P), Sirius XM Holdings (NASDAQ:SIRI), or Penn Virginia (OTC:PVAHQ) from posting sharp gains on the day.

Pandora jumped 14% after its December metrics showed that reports of its impending death at the hands of Apple (NASDAQ:AAPL) had been exaggerated. Many investors had expected that the advent of Apple's iTunes Radio would spell the end of Pandora, but December figures show that Pandora had 76.2 million active listeners in December, breaking its old monthly record and showing 13% growth from year-earlier figures. Listening-hour growth also clocked in at 13%, but the real key for Pandora's future will be whether it can keep effectively monetizing its listeners through ad revenue. If so, then Pandora could have far more staying power than skeptics ever expected.

Sirius XM gained more than 7% on the heels of Friday night's offer from key shareholder Liberty Media (NASDAQ:FWONA) to take over complete control of the satellite-radio company. The all-stock deal came with only a minimal premium to the closing price of Sirius XM shares on Friday, and today's closing price is actually above the value of the offer. That suggests shareholders, who must approve the deal, plan to hold out for more.

Penn Virginia rose 8% after an analyst firm put the exploration and production company on a list of likely takeover candidates this year. With substantial assets in the Eagle Ford shale play in South Texas, Penn Virginia could benefit from acquisition interest in the area. As long as energy prices cooperate, today's gains could be just the initial gusher from a long-producing well of value for shareholders.