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 Zulily (UNKNOWN:ZU.DL) gained 4.5% in premarket trading Wednesday after Goldman Sachs upgraded the online retailer from neutral to buy.

So what: Along with the upgrade, analyst Taposh Bari raised his price target to $50 (from $47), representing about 37% worth of upside to yesterday's close. So while momentum traders might be turned off by Zulily's sharp decline since late February, Bari's call could reflect a sense on Wall Street that its growth prospects are just too cheap to pass up.

Now what: According to Goldman, Zulily's risk/reward trade-off is rather attractive at this point. "With the stock off 46% from its February 28 peak on the back of sector multiple compression and its lock- up expiration, we see a good entry point as the company expands its merchandising, fulfillment, and marketing initiatives which we expect to drive higher-than-expected customer growth into 2015," said Bari. Given Goldman's solid call-making track record -- currently ranked in the top 15% of our CAPS community -- growth-oriented Fools might want to take a closer look at Zulily.