While Fools should generally take the opinion of Wall Street with a grain of salt, it's not a bad idea to take a look at particularly stock-shaking analyst upgrades and downgrades -- just in case their reasoning behind the call makes sense.

What: Shares of Nimble Storage (NYSE:NMBL) soared 8% this morning after Morgan Stanley upgraded the flash storage technologist from equal-weight to overweight.

So what: Along with the upgrade, analyst Katy Huberty planted a price target of $38 on the stock, representing about 36% worth of upside to yesterday's close. So while momentum traders might be turned off by Nimble's sharp pullback in recent months, Huberty's call could reflect a sense on Wall Street that the concerns surrounding its growth trajectory are becoming overblown.

Now what: According to Morgan, Nimble's risk/reward trade-off remains rather attractive at this point. "We raise revenue estimates above consensus and upgrade NMBL to OW with a $38 PT," said Huberty. "Our recent meetings with management highlight: 1) new products will increase enterprise penetration, 2) Nimble's competitive moat is intact and sustainable, and 3) gross margins remain stable." More importantly, when you consider Nimble's rock-solid balance sheet and still-beaten stock price, the downside seems limited enough to bet on that upbeat outlook.