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: Seagate Technology (Nasdaq: STX) dropped 18% in intraday trading today after issuing a disappointing outlook for the current quarter.

So what: For its just-completed quarter, EPS of $0.28 handily beat the $0.25 consensus estimate. But for the current quarter, management guided to EPS of $0.29 to $0.33, well below the $0.44 consensus estimate and EPS of $0.37 in the year-earlier quarter.

Now what: Revenue guidance for the current quarter was in line with expectations, but the cost of certain rare earth materials sourced from China has soared dramatically and become quite volatile in recent months. While management stated it thinks there is currently a bubble for those materials, the situation adds an element of unpredictability -- in both directions -- to Seagate's outlook. What's more, yesterday evening Intel (Nasdaq: INTC) cut its forecast of PC unit shipment growth from 15% to between 8% and 10%.

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Fool contributor Cindy Johnson does not own shares of any company named above. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.