I follow quite a lot of companies, so the usefulness of a watchlist for me cannot be overstated. Without my watchlist, I'd be unable to keep up with my favorite sectors and see what's really moving the market. Even worse, I'd be lost when the time came to choose which stock I'm buying or shorting next.

Today is Watchlist Wednesday, so I'm discussing three companies that have crossed my radar in the past week and at what point I may consider taking action on these calls with my own money. Keep in mind, these aren't concrete buy or sell recommendations, and I don't guarantee I'll take action on the companies being discussed. But I promise that you can follow my real-life transactions through my profile and that I, like everyone else here at The Motley Fool, will continue to hold the integrity of our disclosure policy in the highest regard.

MannKind (MNKD 0.72%)
It's finally crunch time for one of the most polarizing biotech stocks, MannKind, which has a PDUFA decision date less than five weeks away for its inhaled diabetes therapy Afrezza.

The magnitude of this decision can't be understated. On paper, Afrezza makes a lot of sense given that most diabetes patients would prefer an inhaler as opposed to daily injections of insulin. There will always be a group where the opposite is true, but from a mere convenience factor Afrezza makes a lot of senses.

The diabetes market is also enormous, with the Centers for Disease Control and Prevention reporting that 25.3 million people in the U.S. have diabetes and another 79 million are in the pre-diabetes state. Assuming diabetes testing improves, this represents a gigantic moat of opportunity for Afrezza.

The clinical data thus far leans toward the inhaled therapy being approved. MannKind's second-generation inhaler delivered noninferior decrease in A1C levels relative to the placebo, reduced instances of hypoglycemia, and provided a more favorable weight-control profile than the control arm. Still, plenty of questions remain.

One big question is whether MannKind will be able to find a partner prior to its PDUFA decision date. MannKind has been burning through cash at an exceptional rate while developing Afrezza, and a partner, as well as an up-front licensing payment, would go a long way toward validating its therapy.

Another confusing tidbit that Foolish biotech guru Brian Orelli pointed out in February is that the company will not release the full clinical results of its phase 3 study until June at the American Diabetes Association meeting. In other words, although the FDA gets a look at MannKind's complete data set for its decision on or before April 15, you as the investor don't prior that decision. If I were a shareholder, that would be a bit unnerving.

One thing is for certain: A big move has been built into MannKind's share price based on this decision. I suggest you keep a close eye on MannKind over the next couple of weeks, as this therapy has make-or-break potential.

Mobile TeleSystems (MBT)
There aren't many Russian-based companies trading on the U.S. stock exchanges, but those few have seen significant upheaval over the past couple of weeks as tensions between Russia and the Ukraine have intensified. The territorial dispute and the potential for armed conflict in the region threaten to hurt growth prospects not only in Russia and Ukraine, but throughout the rest of the world.

Perhaps no sector has been hit harder than Russian telecoms, including providers Mobile TeleSystems and VimpelCom (VEON 0.55%). The thinking from short-sellers and pessimists is that regional strife will tighten spending and slow expansion in a region that's already highly saturated with mobile phones. VimpelCom is already suffering after it announced in January a greater-than-95% reduction of its dividend, leaving just $0.035 per share annually when it had been guiding investors toward an annual payout of $0.80 per share just weeks prior. VimpelCom noted that the dividend cut is being made to help pay down existing debt that was acquired through a number of recent acquisitions.

However, things at Mobile TeleSystems, or MTS for short, are looking up. In early February, just a week after VimpelCom devastated income investors, MTS affirmed that the overall Russian telecom market is on pace to grow by 3% annually between 2013 and 2016. This led MTS to announce its three-tiered strategy for success that involves focusing on data (i.e., improving its infrastructure to give users the fastest network possible), differentiation through unique products and services, and the expectation of higher dividends in 2014 and 2015. 

Another factor to consider here is that while the Russian and Ukrainian markets are highly saturated, a number of regions are still reliant on slower 3G or even 2G technology. This leaves MTS with ample opportunity to see high-margin data plan growth as 4G and next-generation 4G LTE find their way into the region and consumers upgrade to smartphones. Recently Russia's MegaFon struck a deal to sell Apple's iPhone in Russia, and I would anticipate that a bigger push into the nation could be right around the corner. If MTS were to hook up with Apple, it's quite possible that its data margins would benefit in a big way.

If MTS continues to weaken due to the potential for conflict, it could make for an intriguing buy.

Plug Power (PLUG -6.95%)
As we do every week, I have a company (certainly not for the faint of heart) that short-sellers may want to keep their eyes on -- in this case, it's Plug Power.

Plug Power is a fuel-cell systems developer that has seen its stock surge by more than 5,000% over the past year (Plug traded at just $0.12 a year ago) on the heels of optimism surrounding the viability of fuel-cell systems, as well as a recent order win.

The primary driver in Plug's share price has been the 1,738 fuel-cell unit order from Wal-Mart (WMT 1.32%) to provide the power for forklifts in select regional warehouses throughout the United States. The order could go a long way in validating the long-term usage of fuel cells and might even inch Plug Power closer to becoming profitable.

Not to discount the company's achievement in bagging an elephant of a client like Wal-Mart, but the reality is that Plug Power's contract orders are often lumpy at best and that it's still not turning a profit on a trailing basis. In fact, over the past decade Plug Power has produced a free-cash outflow of $409 million as shareholders have witnessed the erasure of practically its entire book value. Plug Power's current book value is a paltry $0.02, down from $34 in 2006. 

Based on Wall Street's present estimates, Plug Power is likely to bring in around $60 million in revenue in fiscal 2014, yet its valuation topped $1.1 billion this week. Although it's possible that Plug could remain in the stratosphere longer than short-sellers can remain solvent, I feel it's safe to begin assuming that the fundamental prospects and its current price don't make a lot of sense. I would suggest adding Plug Power to your watchlist and perhaps looking for a short-sale entry point after things have calmed down a bit.

Foolish roundup
Is my bullishness or bearishness misplaced? Share your thoughts in the comment section below and consider following my cue by using these links to add these companies to your free, personalized watchlist to keep up on the latest news with each company: