Investors often turn to recommendations made by Wall Street analysts before making a Buy, Sell, or Hold decision about a stock. While media reports about rating changes by these brokerage-firm employed (or sell-side) analysts often affect a stock's price, do they really matter?Let's take a look at what these Wall Street heavyweights have to say about Petrobras (PBR) before we discuss the reliability of brokerage recommendations and how to use them to your advantage.Petrobras currently has an average brokera ...