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 RealD (NYSE: RLD) fell as much as 10% in early trading, on speculation that the new Harry Potter movie, while already a smash for Time Warner (NYSE: TWX), isn't drawing much in the way of 3-D sales.

So what: Color me sympathetic to the sellers' plight. I mean, if Harry Potter isn't better in 3-D -- or at least enough of an improvement to merit the extra charge -- then there's little chance of RealD convincing strapped theater operators to buy more of its stereoscopic screening gear.

Now what: With the exception of poorly received superhero epic Green Lantern and the latest in Michael Bay's Transformers series, 3-D hasn't been much of a draw at the summer box office. Other big-name flicks -- including Pirates of the Caribbean: On Stranger Tides, Kung-Fu Panda 2, and Cars 2 -- saw less than 50% of receipts come from more expensive 3-D showings.

Maybe big names and big effects just aren't enough to get consumers to pay for the sort of immersive viewing RealD promises? I wouldn't be surprised -- the experience still demands glasses that haven't changed much since the 1950s. Do you agree? Disagree? 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 owned shares of Time Warner 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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