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 chipmaker Xilinx (NASDAQ:XLNX) plummeted 15% today after its quarterly results and outlook disappointed Wall Street.

So what: Xilinx's Q1 EPS of $0.62 managed to edge estimates, but a wide miss on the top line -- revenue of $612.6 million versus the consensus of $631 million -- coupled with downbeat guidance, reinforces concerns about softening demand going forward. While management's cost reduction efforts resulted in a year-over-year improvement in both gross and operating margin, analysts are worried that unfavorable wireless infrastructure trends will continue to dampen Xilinx's growth prospects.

Now what: Management now expects Q2 revenue to be flat to down 4% sequentially, versus the average analyst estimate of 2.2% growth. "June quarter revenues were affected by weaker than anticipated sales from our defense and wireless businesses," said President and CEO Moshe Gavrielov. "Looking ahead to the second half of our fiscal year, I believe Xilinx is positioned to benefit from a recovery in wireless and defense programs as well as improved business conditions in wired communications and industrial applications." When you couple the wireless headwinds facing Xilinx with its steepish PEG above 1.5, however, I'd hold out for an even wider margin of safety before buying into that turnaround talk.