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 Amazon.com (NASDAQ:AMZN) slipped 1.5% this morning after UBS downgraded the Internet retail gorilla from buy to neutral.

So what: Along with the downgrade, analyst Eric Sheridan lowered his price target to $375 (from $450), representing about 4% worth of upside to yesterday's close. While contrarians might be attracted to the stock's late-January pullback, Sheridan thinks that Amazon's appreciation prospects remain limited given the surprisingly negative results of its recent consumer survey.

Now what: According to UBS, Amazon's risk/reward trade-off is pretty unattractive at this point. "Our survey results call into question our prior views about the value that a broad set of consumers are applying to the current iteration of Amazon Prime," noted Sheridan. "If Amazon were to raise Prime fees, such a fee increase might need to be accompanied by either a) a higher level of value in the service offering (additional media content, streaming music and/or Fresh (supermarket) offerings) and/or b) an increased level of marketing around the perceived value of Prime to the general public." Of course, with Amazon now off about 15% from its 52-week highs, those concerns might be providing long-term Fools with a high-quality growth opportunity.