At The Motley Fool, we poke plenty of fun at Wall Street analysts and their endless cycle of upgrades, downgrades, and "initiating coverage at neutral." While the pinstripe-and-wingtip crowd is entitled to its opinions, we've got some pretty sharp stock pickers down here on Main Street, too. (And we're not always impressed with how Wall Street does its job.)

Given this, perhaps we shouldn't be giving virtual ink to "news" of analyst upgrades and downgrades. And we wouldn't -- if that were all we were doing. Fortunately, in "This Just In," we don't simply tell you what the analysts said. We also show you whether they know what they're talking about.

Today, we're going to take a look at three high-profile ratings moves on Wall Street: A sell rating on the Bank of Ireland (NYSE: IRE), balanced by an upgrade for Western Digital (NYSE: WDC) and a price target hike at Westport Innovations (Nasdaq: WPRT).

Irish eyes are crying
Let's get the bad news out of the way first. By now, you've probably heard about Greece's historic debt default/economy-saving deal with lenders. So, crisis averted, right? Europe is saved, and we can all stop worrying about the economy over there?

Not so fast. Turns out there's still a lot of risk in many places -- and in at least one of the banks that lends to them. This morning, Citigroup decided to rate one such bank a "sell": Bank of Ireland. Now, details on this rating are still lacking. While most major news outlets agree that the rating is "out there," no one seems to know why Citi chose now as the best time to advise selling -- but I think we can guess.

Lacking a dividend and selling for a price-to-sales ratio more than twice as big as our own Bank of America (NYSE: BAC), Bank of Ireland is no bargain. Indeed, odds are that if subjected to a stress test like the one that B of A just passed, B of I wouldn't be so lucky. Yet post-Greek bailout, the stock's up more than 50% from its December lows. If you've made a profit from the move, I think Citi's making the right call here. Cash it in. Sell the stock.

Western Digital, ho!
In happier news, hard-disk drive-maker Western Digital scored an upgrade from Needham & Co. Western D, as you may be aware, is the major HDD rival to Seagate (NYSE: STX), which won multiple buy ratings of its own last month in the wake of a monstrously profitable fiscal Q2 earnings report. After re-examining the effect of its purchase of Hitachi's HDD business, Needham now thinks Western-D's shares are worth 32% more than previously believed -- $66 apiece. And as the stock only costs $40 and change today, that's enough to move the stock from a "buy" to a "strong buy" in Needham's opinion.

I agree. Priced at 14 times trailing earnings and less than 11 times free cash flow, Western Digital shares are priced at just a fraction of what they're worth, if the company manages to hit the 20% growth rate Wall Street has set for it. Factor in the $3.7 billion in net cash on the balance sheet, and the stock's even cheaper than it looks. Fact is, I'm so certain Western Digital will outperform the market from this point onward that I'm going to put my reputation on the line and publicly rate this stock an "outperform" on Motley Fool CAPS. Follow along and see how the pick works out.

Hmm. Move it a little more to the West
And speaking of things that "worked out," last night, FastMoney was giving Westport Innovations some CNBC love. One guest on the program mentioned the natural gas engine-design shop as a natural play on the coming natural gas revolution, and apparently Wall Street was watching. This morning, analysts at JMP Securities upped their price target on the stock by 12.5% to a new objective of $54 per share.

Westport has, as a result, pretty much sidestepped today's market downturn, actually gaining a few cents in share price. But does this mean you should buy the stock?

Not necessarily. Listen, Fools: Westport has a future, and probably a long one. The company just raised $274 million in new capital last month, and even at today's $27 million annual cash-burn rate, that's going to be enough to keep Westport going for many years to come. It gives the company a chance to prove itself a worthy investment.

For the time being, however, Westport is still burning cash. It's not a profitable business. It's not a safe investment -- it's a speculative one. Big risk, big potential reward.

You don't have to bet the ranch to profit from a bullish stock investment, though. If Westport sounds too risky for you, read this (free) Fool report instead, and we'll tell you all about "The Only Energy Stock You'll Ever Need."

Whose advice should you take -- mine, or that of "professional" analysts like Citi, Needham, and JMP? Check out my track record on Motley Fool CAPS and compare it to theirs. Decide for yourself whom to believe.