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 LoopNet (Nasdaq: LOOP) surged 28% on Thursday after real estate research provider CoStar Group (Nasdaq: CSGP) agreed to acquire the real estate listing service for about $860 million in cash and stock.

So what: The deal, in which LoopNet shareholders will get $16.50 in cash and 0.03702 shares of CoStar common stock for each share held, represents about a 31% premium to LoopNet's Wednesday closing price. As CoStar Founder and CEO Andrew Florance believes, the marriage of the two complementary companies "will lead to even more innovation and greater efficiencies by creating the premier Internet solution for the commercial real estate industry."

Now what: While LoopNet shares are probably all popped out, CoStar might be worth a closer look. With very little overlap between its customer base and LoopNet's, CoStar -- which will now have a database of roughly 2 million active listings -- should be able to double its subscribership from the deal. And if Mr. Market's reaction to CoStar's move is of any indication (its shares are also up nicely today), the price it's paying for that added scale is also pretty attractive.

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