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: Ameresco, Inc. (NYSE: AMRC) dropped 12% in intraday trading today after the energy services company's fourth-quarter EPS beat by $0.02 but 2011 guidance fell short of consensus expectations.

So what: Compared to the year-ago quarter, fourth-quarter revenue grew 34%, operating income grew 11% and net income fell -- yes, fell -- 20%. Increases in cost of sales, interest expenses, the effective tax rate, and the share count (related to last October's IPO) all contributed a whopping 37% decline in EPS.

Now what: The mid-point of 2011 guidance calls for growth of 13% in revenue, 14% in EBITDA, 25% in net income and 12% in EPS. The higher share count from the IPO will anniversary out in October 2011, setting the stage for better EPS growth in 4Q11 and 2012. That said, the forward P/E ratio of 19.1x looks steep for a company with revenue and EBITDA growing at a low-teens rate and EPS that is sensitive to fluctuations in interest rates and foreign currency.

Interested in more info on AMRC? Add it to your watchlist here by clicking here.

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.