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.

Stocks opened the week on a positive note, with strong data on U.S. factory and industrial activity pointing to a recovery in manufacturing. European data confirmed those gains, although growth rates slowed in China. Nevertheless, even though major market benchmark posted solid advances, Primero Mining (NYSE:PPP), Cooper Tire & Rubber (NYSE:CTB), and Plug Power (NASDAQ:PLUG) all lost ground today.

Primero Mining fell almost 7% as the company announced that it would buy out Brigus Gold (UNKNOWN:BRD.DL) in a stock-swap deal. Under the arrangement, Brigus shareholders will receive 175 shares of Primero for every 1,000 Brigus shares they own now, and will also get a total 90% stake in a spun-off company that will keep certain Brigus assets largely separate from the combined company. Deals like this might become commonplace as various small producers look for ways to survive lower gold prices, and Brigus Gold shareholders seem happy with the arrangement as its stock jumped 33%.

Cooper Tire & Rubber dropped 5% as a court dismissed the company's lawsuit against India's Apollo Tyres. Cooper has sought to force Apollo to go forward with a proposed merger with the company according to its original terms, but Apollo wants to renegotiate a lower price. Without a court decision in Cooper's favor, the big question now facing Cooper is whether Apollo will agree to make a lower bid or simply walk away from the acquisition entirely.

Plug Power declined 7%, giving back some of its huge gains over the past few weeks that have resulted in the stock's price quadrupling since early November. Promises of a "blowout quarter" with hints of a deal with a major potential customer have raised hopes among the hydrogen fuel-cell power provider. But investors today might well have remembered that Plug Power has made similarly positive forecasts in the past without ever realizing its full potential. With rivals already having substantial sales and backlogs, Plug Power needs to deliver on its promises this time if it wants investors to take its recent jump seriously.

Fool contributor Dan Caplinger has no position in any stocks mentioned. You can follow him on Twitter: @DanCaplinger. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.