If you're Microsoft (NASDAQ:MSFT), that warm breath you're feeling on the back of your neck isn't a surprise anymore. You don't even need to peek over your shoulder. You know it's Google (NASDAQ:GOOG), sneaking up on you again.

This week's new threat -- the launch of Google Apps for Your Domain -- allows domain owners the ability to incorporate several organizational features like Google Mail, Google Talk, Google Calendar, and Google Page Creator into their actual domain names.

It may sound like a mouthful, but it's really Google integrating itself deeper into the lives of small and medium-sized businesses and organizations at the expense of the popularity of Microsoft applications like Outlook and Exchange.

The battle to end all battles
When Microsoft's chief executives huddled together for a tactical summit last year, the "Google Challenge" may have seemed like an overdone doomsday scenario. Most see Google more as an opportunity than as a challenge, but Mr. Softy knew better. As far as Microsoft is concerned, just about everything Google has been rolling out is a threat. You know what? Microsoft is absolutely correct.

Google Desktop and its toolbar? It's Google's way of embedding itself into your system, replacing file searches and browser functions that Microsoft once owned. Google's teaming up with Sun Microsystems (NASDAQ:SUNW) to promote Sun's Open Office was a direct affront to Microsoft's Office suite of applications. Any doubts on that front have been laid to rest as Google has moved aggressively in launching Google Spreadsheets and acquiring Writely, a Word rival. Unlike standalone software programs, Google's offerings store data on Google's servers. That facilitates sharing the data with co-workers, as well as giving the creator the ability to access the files from any Web connection. Sure, it gives Google an easel to paint some relevant ads around the edges, but there's no such thing as a free lunch.

Microsoft's software stronghold has been tested in the past. Despite its resurgence, Apple Computer (NASDAQ:AAPL) still commands a tiny slice of the PC pie. When IBM (NYSE:IBM) decided to try its hand at operating system software, OS/2 came on strong, but it has fizzled to little more than a fringe player these days. Linux stormed onto the scene threatening to crush Microsoft with its open-source platform, but it has excelled mostly in the server market. Enterprising players like Red Hat (NASDAQ:RHAT) have gone on to carve out a cozy living in that space without really nibbling away at Microsoft's growth prospects.

If anything, Microsoft's history is loaded with instances when it was actually late to the game in areas like Internet browsers or media-playing software and still ultimately spanked the market leaders silly. Whether Microsoft has been on top or started out at the bottom, rare is the case like the Xbox, where the company remains a serious laggard to the king of the hill once it commits to the fight.

Google is different. It possesses the same mindshare advantage with which many credit Microsoft in its own victories. Microsoft has been able to use its status as the pre-bundled operating system of choice to champion many of its features. Now Google is taking advantage of the girth of its audience to scrape away at many of those Microsoft wins.

Eight-minute apps
Google's creative workplace inspires a self-replenishing supply of appendages to its Google.com search engine workhorse. Occasionally the company hits paydirt, as it has with Google AdSense and Google Maps. When it comes up short, it's only a matter of dusting it beneath the beta rug and cranking up the workstation to start anew with something else.

Google and Microsoft may have different philosophies and come from different backgrounds, but when they're at the same party, they can both spot the hot girl on the dance floor. In a perfect world, they would be two smart kids swapping brainy jokes by the punchbowl. When a girl is involved, animal magnetism kicks in and they become testosterone-addled competitors.

I don't think Google is deliberately gunning for Microsoft. I don't think Microsoft has Google in its crosshairs. They are just each in the way of what the other one wants. The hot girl at the party? She is the monetization of computer usage, and Microsoft and Google both want the next dance. Off in the corner, Yahoo! (NASDAQ:YHOO) is popping an Altoid in its mouth as it builds up the courage to make an outside move. The end result is that each bellwether is seen as collateral damage.

Sure, Google and Microsoft will do some silly things to attract attention. This week, they're flexing their apps. Next week? A data-chugging kegger may be in the works. It will make each company stronger in the end. Competition refines the pickup line.

Think you've got her, Microsoft? Think the soothing breath warming the back of your neck is finally her? Turn around, then. See if she wants you to be her next dance partner. It's not her? You fool. It's only Google, but you probably knew that all along anyway.

Microsoft is a selection in the Inside Value newsletter service.

Longtime Fool contributor Rick Munarriz finds nothing wrong with hanging out by the punchbowl and dishing out punch lines. He does not own shares in any of the companies mentioned in this story. He 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 .