I heart Google (Nasdaq: GOOG), but I'm not stupid. I know that any company that has 99% of its eggs in one basket -- in this case, advertising as a percentage of total revenue -- is susceptible to a nasty slip.

I know that any company brandishing a "do no evil" corporate mantra, just like Gary Hart challenged the media to "follow me around" two decades ago, will get raked over the coals when it's caught in the midst of monkeybusiness.

I also realize that a company with perpetually decelerating growth -- the pros expect Big G's profits to rise just 33% this year -- can be a portfolio risk. Especially if it's trading at too high a premium, and owned by investors who may be too naive to realize that Big G can't kick it old school like it used to.

I'm not about to short Google. I just can't justify buying in when the company's horizon features more uncertainties than opportunities.

Adventures in paid-search babysitting
Google may have revolutionized the field of contextual marketing, but there's no guarantee that its dominance will last. As click fraud and other flaws to the system receive wider media coverage, advertisers may send keyword bids lower. Isn't it just a matter of time before ad blindness kicks in, after Web surfers see one too many "Ads by Google" boxes?

Since most of Google's ad revenue is click-based -- not impression-based or action-based, like you find with display-ad champs DoubleClick or ValueClick (Nasdaq: VCLK) -- can you imagine what would happen if the world just stopped clicking on Google ads, or switched to browsers that could automatically disable them? What would Google be worth then?

Sure, Google is supposed to acquire DoubleClick, but global regulators seem to be sitting on this one for nearly as long as they've held back XM and Sirius from shacking up.

What does it tell you that even the European Commission is poring over Google's $3.1 billion deal for DoubleClick, while longtime European target Microsoft (Nasdaq: MSFT) had no trouble snapping up aQuantive for nearly twice as much? It looks like regulators will keep Google's nonorganic growth on a short leash while letting everyone else beef up.

Cracks in the Google armor
It was a wee sliver, but I couldn't get over a break in the publisher payout trend in Google's last quarterly report. The company relies on a network of third-party sites like MySpace and Time Warner's (NYSE: TWX) AOL to rebroadcast its paid-search ads. It's a great system for Google, serving both as a profitable way to distribute excess inventory and an effective promotion for its own ad platform.

When Google's ads run through third-party sites, the company repays the ads' publishers the bulk of the revenue generated. Here's the trend I noticed:

Network Revenue

AdSense Partner Distributions

APD/NR

Q3 2006

$1.04

$0.780

75%

Q4 2006

$1.20

$0.916

76%

Q1 2007

$1.35

$1.05

78%

Q2 2007

$1.35

$1.06

79%

Q3 2007

$1.45

$1.12

77%

All amounts in billions.

After several quarters of paying out a larger chunk of its AdSense revenue to its publishers, Google decided to pull back during its most recent quarter. Obviously, this trend couldn't keep climbing forever. Still, what if Google is starting to scale back because it senses that keyword bids will decline in the future?

We'll find out whether the trend continues with the fourth-quarter report at the end of this month. How bad would Google's timing be if the company started getting cheap with its publishers just as its rivals fortified their own efforts?

Google is still doing great, but no company is guaranteed a permanent spot as the top Web search provider. In a few years, it might be Facebook, Wikipedia, or even the increasingly Web-present Apple (Nasdaq: AAPL). Heck, it may even be a company that doesn't even exist right now.

Watching Google fight for scraps like radio advertising or print ads has to trouble even the most ardent bull. Has it exhausted its growth potential in higher-margin Web areas? While I see the logic in cashing in on its fat list of willing sponsors, how much longer before Google is down to selling temporary tattoo ads on my forehead?

I have a price, you know. However, like Google's buoyant stock, it's inflated by too much pride, and destined to head lower once humility and desperation kick in.

You're not done with the Duel yet! Go back and read the other entries, share your opinion in CAPS, and vote for the winner.

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Longtime Fool contributor Rick Munarriz is a big fan of Google. It would be his home page if not for Fool.com taking up that slot. He does not own shares in any of the stocks in this story. 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.