Every day of the work week, Wall Street's diligent worker bees dole out dozens of upgrades, downgrades, new ratings, and price tweaks on the ratings they've already issued. Buy this, sell that, aggressively accumulate the other -- the instructions come fast and furious, and judging from the shifts in stock price that follow each, a lot of investors closely follow what the Street's best and brightest have to say about their stocks.

But should they?

This new series, brought to you by Yahoo! Finance, looks at which upgrades and downgrades make sense, and which ones investors should act on. Today, here are three high-profile ratings moves making the rounds on Wall Street: new buy ratings at American Superconductor (Nasdaq: AMSC) and Skullcandy (Nasdaq: SKUL), and a big bump in target price for priceline.com (Nasdaq: PCLN).

It's a bird! It's a plane! It's American Superconductor!
Shares of American Superconductor are leaping tall buildings this morning, helped by a leg-up from Maxim Group. But initiating coverage with a recommendation to buy and a $7 price target (nearly twice what the shares were selling for yesterday), you'd think Maxim would give investors more to go on that what it did.

So why does Maxim think American Super will outperform the market? Citing a 68% fall in share price, the analyst argues that investors are underestimating utilities' need to upgrade their infrastructure for better "grid management" of "sudden voltage changes." As it just so happens, American Super produces voltage regulators that serve this purpose. Plus, the company is apparently close to settling a long-standing dispute with key Chinese customer Sinovel Wind Group. Between the possibility of strong sales going forward, and a potential "lifeline" being offered it by Sinovel, Maxim argues there's every possibility American Superconductor will produce a "positive surprise" that will "drive up the stock materially."

Anything's possible, and Maxim may be right about its hoped-for surprise. But investors need to be aware: This company isn't profitable today. Nor do analysts expect it to earn any profits this year or next. The company's burning cash at the rate of $160 million a year but had just $64 million in the bank at last report. In short, while a surprise is possible, American Super is anything but bulletproof.

This stock goes to 11! (Or maybe even $23)
A better chance for investors to profit comes from the mouth of Northland Securities, which slapped a $23 price target and a recommendation of outperform on trendy earphones-maker Skullcandy. Details on the upgrade are pretty much nonexistent so far, but the numbers do look good here. Cash-rich and nearly debt-free, Skullcandy shares sell for just 21 times earnings, despite consensus estimates that the company will grow its profits at about 25% per year over the next five years.

Skullcandy looks cheap today. If Northland's right about the potential for a 40% gain, Skullcandy really could be as sweet of a deal as the analyst describes.

40% profit? Check!
Of course, if you bought shares of priceline.com a year or so ago, you've already earned yourself a 40%-plus profit. But even if you missed out, there's no need to worry. According to analysts at The Benchmark Co., there's still more profit to be had from Priceline. This morning, the investment banker named a new (target) price for the stock: $840 a share, up from a previous prediction of $692 -- a "prediction" that Priceline actually blew right by weeks ago.

Two things stand out in this new bull thesis, however. First off, aggressive as Benchmark's triple-digit target price sounds, it actually only offers about 12% from today's price. In a world where banks are paying sub-1% interest rates, and bonds can pay less than nothing, 12% is a substantial sum -- but it's not without risk.

Consider: Even at today's price, Priceline shares cost 36 times trailing earnings. That's compared to long-term growth estimates of less than 23% per year. Again, a big number, but probably not enough to justify even today's share price, much less the one Benchmark predicts the shares will fetch a year from now. If you were looking for a reason to "ring the register" on Priceline, Benchmark's upgrade and the extra $8 it just tacked onto Priceline look like the perfect excuse.

Motley Fool contributor Rich Smith does not own shares of, nor is he short, any company mentioned above. The Motley Fool owns shares of Skullcandy. Motley Fool newsletter services have recommended buying shares of priceline.com.