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 mattress maker Tempur-Pedic International (NYSE: TPX) plunged a whopping 47% on Wednesday after management slashed its current-quarter and full-year guidance.

So what: Tempur-Pedic was one of the market's hottest stocks over the first three months of 2012, but the gloomy outlook reinforces recent fears over rapidly intensifying competition in North America. Unfortunately, those concerns are being compounded by disappointing results today from rival Mattress Firm Holding (Nasdaq: MFRM), all of which are working to push down the shares of Sealy (NYSE: ZZ) as well.

Now what: Tempur-Pedic now expects full-year EPS of $2.70 on revenue of $1.43 billion, well below Wall Street's view of $3.93 and $1.64 billion, respectively. "We are projecting lower sales than previously anticipated for the rest of the year and are taking actions to realign our expense structure appropriately," said CEO Mark Sarvary. "However, we remain very confident in our Company's growth potential and our strong brand, and as a result remain committed to our long-term strategic plan." With the stock now down a staggering 75% from its April highs, brave bargain-hunters might want to consider buying into that optimism.

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