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 Millenial Media, (NYSE: MM) plunged more than 14% Thursday after the company turned in disappointing forward guidance.

So what: Adjusted fourth-quarter revenue rose 44% year over year, to $109.5 million, which translated to adjusted net income of $0.08 per share. On a GAAP basis, Millenial Media turned in a net loss of $0.04 per share. By contrast, analysts were looking for a loss of $0.05 per share on sales of $95.62 million.

However, the company also expects total revenue in the current quarter to be in the range of $72 million to $76 million. Analysts, on average, were looking for significantly higher first quarter revenue of $83.25 million. Adjusted EBITDA is also expected to come in at a loss between $5 and $6 million.

Now what: Millennial Media's fourth-quarter results were decent, but there's no denying that our market is a forward-looking machine. With shares currently trading at a lofty 23 times this year's estimated earnings -- and keeping in mind those estimates are likely to fall as analysts have time to fully digest today's news -- I think investors would be wise to simply watch from the sidelines for now.