Is $450 the next stop on the Google (NASDAQ:GOOG) freight train? Nearly a dozen analysts raised their estimates on the dot-com giant after the company's blowout third-quarter report. Three in particular -- Lehman Brothers, First Albany, and RBC Capital Markets -- declared $450 as the high-octane stock's new price target.

I can go off on price targets, the often ludicrous stuffed rabbits that analysts whisk around the oval racing track to tempt drooling four-legged investors. I guess I just did. However, ranting against puffy round phantom numbers isn't my intended target this time. Let's just call that passing shot collateral damage.

See, I am more concerned about the plausibility of Google hitting $450 in the near-term. It won't be easy. Yes, I am fully aware that Google went public at $85 just 14 months ago and has gone on to quadruple to $340. What's another 32% spurt in the grand scheme of things?

Plenty. No, I'm not bearish on Google. I've got a schoolboy crush on the online juggernaut. I'm carving "Munarriz Loves Google" on my desk with a penknife and I'm really hoping it'll let me take it to the prom in the spring. My problem is that we can't assume that Google's trajectory will continue skyward unchecked.

The company closed out its third quarter with 290 million diluted shares outstanding. That includes just a weighted sliver of the more than 14 million freshly minted shares that were sold by the company last month. So we're talking about a company with more than 300 million fully diluted shares out there at the moment.

We're talking about Google needing to be valued at nearly $33 billion more to earn that $450 price tag. If you had $135 billion burning a hole in your pocket, would swallowing Google in its entirety at $450 a share seem like a more prudent scheme than backing up the truck and loading up on penny candy and Twizzlers?

Winning the $450 betting pool
Yes, Google will be a $135 billion company someday. I believe it. It's why I think that shorting Google would also be a brutal mistake. It's just that the actual "Hey, Google hit $450" day may not come over the next few months or even over the next few quarters. Don't worry, I'll show my math.

Over the past four quarters, Google has generated an impressive $1.3 million in net profits. The $450 argument would seem to claim that Google is growing so quickly that paying better than 100 times that bottom line sum is a reasonable trade.

If we go by Google's awesome report from Thursday afternoon, where revenues soared by 96% and net profits grew even faster, it's easy to get excited. This is a scalable business, and the migration of marketers to the online platform is just getting started.

However, what does the future hold for Google? It has generated a whopping $5.3 billion in advertising sales over the past year, but how much more will it have to grow its top line to justify a $450 sticker price?

I'm asking this only because Google is going to be challenged in its efforts to keep growing. Until now, Google and Yahoo! (NASDAQ:YHOO) have ruled the lucrative keyword-based paid search goldmine, but it's now attracting new miners. Microsoft (NASDAQ:MSFT) is beta testing its AdCenter, while InterActiveCorp (NASDAQ:IACI) began selling paid listings on its popular Ask Jeeves search engine last month.

Google wallpapered the Web with its AdSense program, which allows even the smallest of content sites to duplicate Google ads on their sites. But now Yahoo! is starting to accept small publishers in its Yahoo! Publisher Network.

With companies like Motley Fool Stock Advisor recommendation TiVo (NASDAQ:TIVO), video game advertiser Massive Incorporated, and even digital billboard specialists all drumming up creative tweaks to interactive advertising, we also can't assume that Google's competition for thicker slices in the sponsorship pie will only be coming from its search portal rivals.

Online advertising is perfect. It's targeted. It can be tracked. It works. However, the plethora of new opportunities for marketers may lead to advertisers learning to bid smarter on keywords. In other words, even if Google is able to grow its own page views and ad clickthroughs, the path to the necessary growth rates to justify a lofty valuation may still pose a challenge. Just because Yahoo! and Google overcame the malady that toppled smaller peers in the paid search space like Miva (NASDAQ:MIVA) and Looksmart (NASDAQ:LOOK) doesn't mean that they may be immune in the future.

Google's own ad revenue is growing faster than its AdSense revenue. That's great on the surface. That's where the fat margins hang out because Google is not having to dole out the majority of that change to third party publishers. However, that may also be a sign that third party sites are being lured elsewhere. From Yahoo! to Chitika's eMiniMalls to whatever product Microsoft ultimately serves up, Google helped monetize the Web for many of the Internet's popular fringe sites, but it's a victim of its own success. The competitive crowds are circling around.

Google is going to make it. Google will be a more important company five years from now than it is today. However, that doesn't mean that it will be that much more valuable once investors adjust their premiums to slower growth rates.

Yes, Google is gold, but the fact that gold is worth more than $450 an ounce these days doesn't mean that shares of Google will be afforded the same luxury in the near term.

Longtime Fool contributor Rick Munarriz thinks that Google got robbed when it wasn't added to the S&P 500 recently. He does not own shares in any of the companies mentioned in this story. The Fool has a disclosure policy. Rick is also part of the Rule Breakers newsletter research team, seeking out tomorrow's ultimate growth stocks a day early.