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) dropped as much as 10.1% today on moderately heavy trading.

So what: There's nothing new with Barnes & Noble itself, but longtime rival Borders Group is going through a high-profile case of bankruptcy-itis. Borders's announcement of new financing, additional store closings, and a tighter e-book partnership added up to sour grapes for other bookish retailers, including Barnes & Noble

Now what: Barnes & Noble's mid-February rally came to a grinding halt following a terrible financial report and a suspended dividend, and the stock trades some 43% lower nowadays. Fellow Fools have compared Barnes & Noble to the beleaguered heroes of Battlestar Galactica, beset on all sides by and Google, to name just two digital giants that are invading Barnes & Noble's traditional home turf. I see traditional bookstores of all stripes emulating an even more depressing role model.

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