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: QuinStreet (Nasdaq: QNST) dropped 23% in intraday trading today after issuing disappointing guidance.

So what: Management surprised investors with a midquarter press release and conference call announcing that revenue for the quarters ending in June and September is likely to be flat year over year. The consensus forecast was calling for growth of 16% and 12%, respectively. The revenue miss is likely to drive an EPS disappointment, too.

Now what: Management blamed current weakness on the auto insurance and financial services segments. Nonetheless, it expects revenue to grow about 15% in fiscal 2012 (which ends in June 2012) and EBITDA margins to expand to 20%. The new guidance suggests EPS growth could slow from 30% over the 12 months that ended in March to about 12% for fiscal 2011 (which ends in June 2011) and about 12% again in fiscal 2012.

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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.