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

What: Shares of Facebook (NASDAQ:FB) rose 1% in premarket trading Thursday after Evercore Partners upgraded the social networking giant from equal weight to overweight.

So what: Along with the upgrade, analyst Ken Sena raised his price target to $75 (from $69), representing about 24% worth of upside to yesterday's close. So while momentum traders might be turned off by Facebook's price pullback in recent months, Sena's call could reflect a sense on Wall Street that its growth prospects are now too cheap to pass up.

Now what: According to Evercore, Facebook's risk/reward trade-off is rather attractive at this point. "The upgrade considers the recent pull-back (in spite of an exceptionally strong quarterly result) and new work on FB's mobile ad networking initiative (FB Audience Network), which this report explores," said Sena. "In a nutshell, FB now monetizes mobile time spent to the tune of 9:1 the industry (x-Search) which supports the notion that FB can meaningfully increase the size of the mobile advertising pie (versus just taking share)." When you couple those prospects with Facebook's cash-rich balance sheet and still-reasonable PEG of 1.1, it's tough to disagree with Evercore's upgrade. 

Brian Pacampara has no position in any stocks mentioned. The Motley Fool recommends Facebook. The Motley Fool owns shares of Facebook. Try any of our Foolish newsletter services free for 30 days. 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.