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 Coupons.Com Inc. (NYSE:COUP) were getting torn apart today, falling as much as 16% and finishing down 11% following a downgrade by Goldman Sachs.

So what: The venerable investment bank lowered its rating on the online coupon seller from neutral to sell on a valuation basis. Coupons.com trades at a forward P/E of 73 and P/S 12, multiples reminiscent of high-flying, ground-breaking stocks like Tesla or Facebook. Goldman maintained its price target at $19, but Coupons.com shares had gained more than 75% in the past month before today's downgrade, topping $30 at one point. 

Now what: It's rare for analysts to rate a stock as a sell, as investment banks like to stay in the good graces of publicly traded companies to which they can provide other services, so the market may have punished the stock more than it would normally on a downgrade. Goldman is also just one of two research firms covering the company. Based on Coupons.com's current financials and the recent struggles of peers like RetailMeNot, I'd tend to agree with Goldman. This stock is simply too pricey for a company lacking a competitive advantage or a guarantee of long-term growth.

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Jeremy Bowman has no position in any stocks mentioned. The Motley Fool recommends Facebook, Goldman Sachs, RetailMeNot, and Tesla Motors and owns shares of Facebook and Tesla Motors. Try any of our Foolish newsletter services free for 30 days. We Fools don't 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.