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: A123 Systems Inc. (Nasdaq: AONE) popped 12% in intraday trading today after an analyst upgraded the stock.

So what: Goldman Sachs upgraded the stock from "neutral" to "buy." The price target was left unchanged at $9.

Now what: Despite its increasing optimism on the stock, Goldman increased the size of the losses it is forecasting, taking its EPS estimates from -$0.85 to -$1.05 for 2012 and from -$0.50 to -$0.70 for 2013. The consensus estimate for 2011 is -$1.46; there is no consensus forecast beyond 2011. Given earnings expectations, "story" seems to be the key word in Goldman's comment that, "We think the market is now discounting just the current chapter of the story..."

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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.