I love Google (NASDAQ:GOOG). As a daily user of Gmail, Google search, and Google Finance, I can say that the company's innovations have literally (and perhaps sadly) improved my quality of life. But Google's stock? That, I fear.

I'm probably not the first person you've heard express concerns over Google's share price. Skeptics, myself included, have been decrying Google's valuation since its summer 2004 IPO. If you've been a shareholder since that time, you've been treated to greater than 500% returns, while we skeptics seem to have gotten egged.

The fears
But Google's prodigious results haven't led this bear to say "uncle" just yet. Far from it. As if Google's rich valuation weren't menacing enough, the business faces several ghoulish threats that lead me to peg Google as an future market-underperformer. Among others, four obvious threats and challenges spring to mind:

1. Virtually zero barriers to entry
Google's core competency -- search -- has barriers to entry the size of LEGO walls. If two guys starting from their dorm room were able to topple one-time reigning search king Yahoo! (NASDAQ:YHOO), what makes you think that Google itself is any more secure?

Given its history and meteoric rise, Google shareholders should understand this threat better than anyone else. Still, you might be inclined to say that "Google is different. It's too large, too entrenched, and has too much cash to throw at the competition." Again, tell that to old-school supporters of Yahoo! and AltaVista, or, moving laterally, to eBay (NASDAQ:EBAY) shareholders who've fretfully watched the rise of Craigslist.

2. Competition from the other big dogs
Not only does Google face the threat of a multitude of hungry, VC-backed start-ups, but it also has to fend off deep-pocketed peers like Microsoft (NASDAQ:MSFT), Yahoo!, and IAC/InterActiveCorp (NASDAQ:IACI), parent of Ask.com. Google has been kicking those companies' tails in search for the past several years, but Steve, Jerry, and Barry aren't exactly just throwing in the towel.

Furthermore, even as they clamor to one-up Google, the other titans are also pestering Google by chasing many of the same acquisition targets. Look no further than the whopping price Google was forced to offer up for DoubleClick as proof of what can happen when you pit a couple of ludicrously cash-rich companies against each other.

3. An advertising-based model
Virtually all of Google's revenue comes from selling ads. I'll admit that the model can produce incredible margins, and that Google has taken its execution to new heights. That said, binding the company's fortunes so tightly to an approach that has left heaps of corpses in the corporate graveyard is more than a touch frightening.

4. The big-britches problem
Like Microsoft, Wal-Mart (NYSE:WMT), and ExxonMobil (NYSE:XOM), Google has discovered that remarkable success draws a sometimes uncomfortably hot spotlight, which can lead to growing legal bills and PR gymnastics.

In terms of litigation, and despite recent steps to alleviate the risk, YouTube remains a ticking legal time bomb. On the PR front, the company has separately drawn flack from privacy advocates and those who note that the "don't be evil" mantra can sometimes be, ahem, loosely interpreted.

Now, I'm not saying that complaints of either the legal or punditesque kind will be Google's downfall, but don't surprised when the legal bills and ill will toward the company mount in the coming years.

5. The valuation
Boo! Yeah, I know I said that I wouldn't bring up the valuation, but come on: Google trades at around 52 times earnings. Fools ignoring a potential investment's valuation would be like an NBA team ignoring a draft prospect's height. Both measures have clear implications on future returns.

Google's shares may not be priced for perfection, but they are priced for what I'll call "sustained awesomeness." It doesn't take much of an operational slip at a 52-P/E company to turn shares into a pumpkin.

Google forecast: Underperformance, with a slight chance of greatness
Again, I love Google, and I have huge respect for the company's accomplishments. The company could innovate itself to outstanding returns for many more years to come. But given the risks outlined above and the fat valuation on the shares, I certainly wouldn't bet on it.

If you agree that Google is the world's scariest stock, head over to CAPS and rate the company an underperform. We'll announce the winning stock on Oct. 31.

Want to know what other companies give us the frights? You can view the rest of our hair-raising stocks here.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.