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 WebMD (Nasdaq: WBMD), which uses the Web to provide health information to doctors and consumers, fell more than 24% on seven times the average volume after the company lowered its full-year revenue outlook.

So what: Third-quarter revenue fell marginally compared WITH last year's Q3 and came in below expectations. Earnings exceeded by $0.07 a share, but lower guidance eliminated whatever goodwill would have come from the beat. Management now sees 2011 revenue of $555 million to $565 million, down from earlier estimates of $580 million to $600 million.

Now what: Both Carl Icahn and George Soros have taken substantial stakes in WebMD in what appears to be hopes that executives will concede to a transaction that values the business at a premium to today's levels. Management is fighting back by adopting a "poison pill" to protect against a hostile takeover. Whose approach do you believe will be best for common shareholders? Please weigh in using the comments box below.

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Fool contributor Tim Beyers is a member of the Motley Fool Rule Breakers stock-picking team. He didn't own shares in any of the companies mentioned in this article at the time of publication. Check out Tim's portfolio holdings and Foolish writings, or connect with him on Google+ or Twitter, where he goes by @milehighfool. You can also get his insights delivered directly to your RSS reader.

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