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 Barnes & Noble (NYSE:BKS) shot up as much as 27% today after news broke that Microsoft (NASDAQ:MSFT) may be planning on buying the bookstore-chain's Nook e-reader unit outright.

So what: Microsoft had purchased a 16.8% stake in the Nook last year for $300 million, valuing the unit at $1.7 billion and, last night, tech blog TechCrunch reported that Microsoft may put in a bid for the rest of the e-reader's digital assets at $1 billion, according to the company. Barnes & Noble also said that it plans to stop making the Android-based Nook tablet by the end of 2014, and rely instead on third-party partner devices.

Now what: If the deal goes through, the $1 billion would certainly be welcome for B&N, which had a market cap just north of that amount before today's surge, but selling the Nook would seemingly only hasten the bookseller's demise. Amazon.com has targeted brick-and-mortar booksellers above all other retailers, and has already consigned Borders to history's dustbin. Nook continues to operate at a loss, but it is still seen as carrying most of Barnes & Noble's market value. Meanwhile, analysts expect losses per share of more than $1.00 this year and next for Barnes & Noble as a whole. I'd say now's a great time to sell. This looks like an excellent example of "buy the rumor, sell the news." Stay on track of this developing story by adding Barnes & Noble to your Watchlist here.