Google ( GOOG) is putting even more of its weight into promoting its Checkout service.

The search giant kicked off a plan earlier this month to offer $10 discounts for first-time users of Checkout, which lets Web surfers make purchases on the Internet in a few easy clicks.

And earlier this week, Google began promoting its new offer by plugging it in what may be the most premium territory on the Internet: An ad for Checkout is now posted on Google's home page, directly under the search box. Search results for some retail items also display a link that allows users to rerun the search incorporating only results for vendors under the Checkout umbrella.

The $10 discount will be available to new users until Feb. 15, and follows on the heels of discount offers up to $20 during the 2006 holiday season . In November, Google also announced that it would extend its offer to waive processing fees for merchants through 2007.

Google's ramped-up efforts will have implications for other major Internet players, most notably eBay ( EBAY), which owns PayPal, a fast-growing rival payment service that currently leads the market.

For now, PayPal has yet to feel the heat from Checkout, despite many predictions of PayPal's demise when Google launched its own service last June. PayPal's adoption rate (the percentage of respondents who said they used the service) of 42% is seven times greater than the 6% for Google Checkout, according to a report released Wednesday by JPMorgan.

Checkout has also had its share of problems , and only 19% percent of users report being pleased with their experiences with the service, as compared with 42% of PayPal users.

Still, the Checkout service is an infant compared with PayPal, which spent eight years and hundreds of millions of dollars in venture capital getting to its current position. And while it may not be displacing PayPal yet, Checkout is off to a strong start, thanks to Google's solid backing, wrote JPMorgan analyst Imram Khan. "We believe Google's aggressive promotions and discounting spurred the respectable launch," he wrote.

Handing out cash to users, waving fees for merchants, and getting to ride on Google's homepage may be just what is needed to help Checkout take its game up a notch.

Giving PayPal a run for its money is one thing, but a widespread adoption of Checkout would have far weightier consequences. Google's domination of the search market puts it in a position to route users around particular Web sites entirely, letting Web surfers zig-zag around the Internet when looking for items. The growth of that type of purchasing behavior will take a heavy toll on e-commerce companies like eBay and ( AMZN).

Google rival Yahoo! ( YHOO), which maintains a retail outlet on the Stores section of its Web site may also feel the impact.

Google's latest bid to boost Checkout demonstrates the enormous resources the company has at its disposal. Highly profitable and deep pocketed, the company can afford to lose money offering promotions on a product that it considers to be strategically important.

And while Google remains highly judicious about using its home page to promote the roughly 85 products it's developing so as not to degrade the user experience, the company does have an enviably visible platform for when it decides to really get behind one of them. In December, Google's home page passed Yahoo! as the second-most-visited on the Web, trailing only Microsoft ( MSFT).

The last three Google products given the privilege to grace the company's homepage -- Desktop, Toolbar, and Pack -- have all seen widespread adoption. Like Checkout, all three also give Google an important toehold that can allow the company to increase its presence in new ways.

Still, the Checkout push also reveals Google's obstacles in pushing one of its products too aggressively. With its unique position as the unbiased navigator of users on the Web, Google is supposed to usher surfers to the destinations that most suit their needs, regardless of who stands to benefit from the direction. With its unparalleled emphasis on placing the experience of its users ahead of all else, Google receives scorn when observers feel it is being too heavy-handed in pushing one of its own products.

Earlier this month, Google quickly removed a "tips" feature under its search results that had advised users to select the company's offerings over that of rivals. A wave of angry blog postings by users felt the company was violating its mission when, for example, it plugged its own calendar feature to users over results generated by its search algorithm.

The inclusion of a Google Checkout vendor-oriented link in search results has already drawn criticism from some prominent bloggers. "Why does this promotion need to be in the main Google search results? What benefit is it providing Google searchers?" wondered Danny Sullivan of the blog Search Engine Land. "I see nothing in that line that's seriously designed to help the search experience. I see only Google self-interest in doing it."

Google may well respond that the Checkout search link allows users to narrow down the list to destinations that allow for the quick, easy purchase of items the user is searching for. But the search giant doesn't need to furnish a pat answer in the future. Google's monomaniacal focus on the search experience was a business decision rooted in a time when the company had only one real product.

As its stable of products grows, the benefits of being able to promote its choicest products will outweigh the small cost of crowding its home page or search results. Recently, the company seems to have dropped maps from rivals like Mapquest and Yahoo! for users searching for locations, choosing instead to solely feature its highly successful Google Maps products.

In the future, the company will grow increasingly likely to tell critics of decisions like the one made with Maps to just get lost.