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 upgrades and downgrades -- just in case their reasoning behind the call makes sense.

What: Shares of Google Inc (NASDAQ:GOOGL)(NASDAQ:GOOG) opened Tuesday up slightly after FBR Capital initiated coverage on the Internet search gorilla with an outperform rating.

So what: Along with the bullish call, analyst William Bird planted a price target of $674 on the stock, representing about 13% worth of upside to Monday's close. So while contrarian traders might be turned off by Google's price strength in recent months, Bird's call could reflect a sense on Wall Street that its growth prospects still aren't fully baked into valuation.

Now what: According to FBR, Google's risk/reward trade-off is rather attractive at this point. "GOOGL is an attractive large-cap GARP [growth at a reasonable price] media investment with one of the widest moats in media and a good deal of optionality around extending its competitive advantage into display advertising, digital content, travel, and payments," said Bird. "Google offers very attractive exposure to each of the key structural growth areas of the Internet -- namely, search, online video, mobile, and the app economy." When you couple that upbeat outlook with Google's still-reasonable forward P/E of 19, it's tough to disagree with FBR's bullishness.