How safe are your stocks?

That question's meant to inspire a spot check on your portfolio -- perhaps an easy task, if you know what your companies are up to. Maybe you've grown comfortable with their valuations relative to their share prices.

But the real challenge isn't how well you know your investments, but rather how well you recognize potential threats to them. You may not think you're holding on to a buggy-whip factory, but circumstances beyond your control can leave your investments hurtling toward the junkheap before you know it.

A company can fall apart even without doing anything wrong. It just might bump up against a better rival with a superior product, process, or service. Spotting future catalysts is a great way to find new buying opportunities, but today, I'll focus on companies that might take hits, given upcoming product rollouts and recent trends.

Wii Fit vs. Life Time Fitness
Next month's debut of Nintendo's (OTC BB: NTDOY.PK) Wii Fit might appear to be just another fad. Gyms around the country may break a sweat over a lively pilates class or a free weightlifting session, but they'll likely shrug off a $90 plaything.

That would be a big mistake. Like many of Nintendo's far-reaching introductions lately, Wii Fit should entice a broader audience beyond pimply-faced teens. Nintendo DS titles such as Nintendogs and Brain Age have sparked sales to older users, just as Wii Fit for the popular Nintendo Wii console will eat into the fitness-center crowd.

Wii Fit is not a toy. It combines a balance board that monitors weight and body mass index with included software featuring physical games and activities to make workout sessions engaging. Together, the package provides regular and instant progress updates in a way that no pricey gym membership can match.

Meanwhile, Life Time Fitness (NYSE: LTM) is on a roll. The company posted healthy quarterly reports this morning, with revenue and profits climbing 21% and 23% higher, respectively. Membership rosters are climbing, and Life Time Fitness is milking more money out of each member.

Your knee-jerk reaction might be, "No way some $90 plaything can compete with a high-end fitness center!" Going to the gym is a social event. But with pesky gas prices that make driving to the gym as costly as it is cumbersome, the Wii Fit offers an engaging, cost-effective alternative at a time when discretionary spending is bumping up against cutbacks.

Wii Fit vs. Weight Watchers
If you think that gyms will have it tough, put yourself in Weight Watchers' (NYSE: WTW) weighing shoes. Wii Fit pushups and ski simulations are more likely to help you shed weight than give you rock-hard abs, and that's going to eat into Weight Watchers.

Lehman Brothers analyst Karen Howland initiated coverage of Weight Watchers earlier this month with an "Equal Weight" rating. No, I'm not making that up. In a nutshell, the analyst is putting out an uninspiring neutral rating on the stock because she sees membership waning as a result of people turning to exercise and surgery as viable options to the Weight Watchers program.

Weight Watchers feasts on image-conscious moms who feel uncomfortable about brushing up against the buff at the local gym, so Wii Fit will be a huge hit with them for providing the convenient one-on-one home-based workouts they crave.

Blu-ray and Mr. Postman vs. Netflix
I have argued that Blu-ray's victory over HD DVD bought some time for disc-based renters like Netflix (Nasdaq: NFLX) and Blockbuster (NYSE: BBI) in the war over digital delivery. However, that may change, because Blu-ray discs are still stubbornly priced higher than conventional DVDs.

In response, Netflix announced this week that it will raise members' rates for Blu-ray rentals later this year. Will members who enjoy high-def discs at the current rate buy in? Worse yet, next month's postal rate hike will be a burden for a company like Netflix, which subsidizes the round-trip shipping on every disc rental.

Fee hikes usually prompt subscribers to consider alternatives. Blockbuster shed 500,000 subscribers soon after hiking prices last year. Netflix recently upped its year-end subscriber targets, and it's unlikely to get there by raising prices; however, costly Blu-ray disc inventory purchases will hurt margins if membership prices stay the same.

Grand Theft Auto IV vs. Electronic Arts
I'm still figuring out who will be ticked off by next week's release of Take-Two Interactive's (Nasdaq: TTWO) Grand Theft Auto IV. Parents, concerned about the violent games that their kids play? Other parents, concerned that the anticipated game will eat into study time as kids head into final exams? Or Electronic Arts (Nasdaq: ERTS), concerned that it helped a competitor's cause in its botched buyout bid for Take-Two?

Take-Two is used to courting controversy as a marketing tool for many of its games. This time, it got an unlikely assist from EA. When EA offered up $2 billion to acquire Take-Two two months ago, it set the stage for Take-Two to turn down the offer while promoting the late April release of its next hit title.

EA is in a bind. Despite the success of Rock Band, the hit machine hasn't had a hand in recent bestsellers such as Guitar Hero, Nintendo's Super Smash Brothers Brawl, and now Take-Two's GTA4. Some of its latest annual layups -- like Madden NFL 08 -- sold fewer copies than its previous installment. GTA4's release, at a time when consumers can afford fewer games, will only hurt EA more. Oh, and to think it handed Take-Two the bullhorn two months ago. 

You vs. me
You may not agree with all my pans. We all read the tea leaves differently. However, seeking out disruptive technologies -- and analyzing the companies that will benefit and those that will falter -- is at the very heart of the work I do as part of the Rule Breakers analyst team.

The one thing I can't emphasize too much: It's never enough just to keep tabs on your stocks. You have to be on the lookout for external factors that can change any company's internal fundamentals. The safety of your portfolio is at stake.

For more Foolishness:

Netflix, Electronic Arts, and Nintendo are Stock Advisor selections. Take-Two Interactive is a Rule Breakers stock pick. If you want help picking out the future catalysts that will help -- or hurt -- your stocks, a 30-day trial subscription is available for you to see which newsletter fits you like a glove.

Longtime Fool contributor Rick Munarriz is a fan of many of the stocks he feels will be threatened, and that includes being a Netflix shareholder. Rick is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early. The Fool has a disclosure policy.