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 Midwestern banker Marshall & Ilsley (NYSE: MI) slipped more than 10% in intraday trading today as third-quarter earnings missed analysts' expectations.

So What: Like fellow regional banks such as Fifth Third Bancorp (Nasdaq: FITB) and KeyCorp (NYSE: KEY), the financial meltdown and recession have not been kind to M&I's bottom line. For the third quarter, analysts were still looking for a loss from the company, but just $0.26 per share versus the $0.32 loss that the bank ended up reporting.

Now What: As I noted earlier today in regards to sinking Comerica (NYSE: CMA) shares, I think investors tend to put too much weight on the pennies on either side of Wall Street's estimates. This is particularly true for the banking sector right now as management discretion in setting loan loss provisions has been having a significant impact on banks' bottom lines. For a bank like M&I that's working to get back on solid ground, investors should be less focused on the quarterly Wall Street hurdle and more on the bank's credit quality and its ability to rebuild its balance sheet with solidly underwritten loans.

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Fool contributor Matt Koppenheffer does not own shares of any of the companies mentioned. You can check out what Matt is keeping an eye on by visiting his CAPS portfolio, or you can follow Matt on Twitter @KoppTheFool or on his RSS feed. The Fool's disclosure policy assures you no Wookiees were harmed in the making of this article.