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

What: Shares of bookseller Barnes & Noble (NYSE: BKS) were sharply higher today, gaining as much as 15% in intraday trading on the back of strong Black Friday sales reports.

So what: While most of the Black Friday reports were general in nature -- such as the National Retail Federation giving a preliminary report that Thanksgiving-weekend sales jumped 16% from last year -- retail stocks broadly were taking the cue to move higher.

For Barnes & Noble in particular, investors may be looking at the reports that customers were rushing for Amazon.com's (Nasdaq: AMZN) Kindle e-book readers and assuming that that means good news for B&N's Nook as well. A report from The Wall Street Journal last week noted that customers "beelined" for the Nook section of B&N's Union Square location in New York.

Now what: I'm far from sold on the idea that good news for the Kindle is good news for the Nook. Sure, on one hand it could mean that the e-reader market in general is growing and gaining acceptance -- that would be good news for all players involved. However, the success of the Kindle could simply mean that Amazon is happily eating B&N's lunch and will continue to strengthen its market share lead.

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