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 Milwaukee-based bank Marshall & Ilsley (NYSE: MI) were up nearly 13% in intraday trading as investors reacted to a bullish report from Goldman Sachs (NYSE: GS) on the financial sector.

So what: In its report, Goldman upgraded its rating on the entire financial sector to overweight, which was the first time it gave the battered sector that rating since the financial crisis. The analysts noted that a rising economic tide will lift the banks, as will increasing dividends -- which Goldman says will start to come after the second round of banking stress tests. Goldman itself was up 2.7% on the news, and fellow financials Morgan Stanley (NYSE: MS), JPMorgan Chase (NYSE: JPM), Citigroup (NYSE: C), and Bank of America (NYSE: BAC) were also showing gains.

Now what: I think there are a lot of smart folks at Goldman Sachs, so I don't take their call on the financial sector lightly. However, one bank's report on financials does not alone make an investment case for any stock, let alone the struggling M&I. I happen to think that the market may have gotten overly pessimistic on M&I and it could provide a good risk/reward for investors. But investors need to dig in themselves and get comfortable with the bank's balance sheet and issues like its exposure to the troubled Arizona housing market -- not rely on a broad sector call from Goldman.

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