In a press release from HitWise published on CNN Money a few minutes ago, Facebook.com just overtook Google.com as the most visited domain in the USA. This is possibly the most significant milestone in Facebook’s history as a large company. Here’s why:

Most of Google’s revenue comes from their Ad business. Half of it comes from their own properties and the other half from a distributed network of sites. (sounding familiar already I’m sure).

There is a lot of noise around Google’s other apps and experiments, but from a business perspective that’s all it is. Noise. Google is a cash creation machine and the cash is created by the ad network both on and off-site. To give you some perspective, Gmail ranks a distant third among email providers with 37 million uniques vs Yahoo Mail’s 106 million uniques 5 months ago [Comsore].

So Google’s business is relatively simple. It’s a the best search engine in the world and an ad network with themselves as their own biggest customer.

Google built this business by first creating an incredibly hot property that gave it’s users an incentive to provide it with awesome targeting data. Then it built an ad network around the targeting data.

The hardest part about building Google was to create the hot property (the search engine) that incentivises users to keep coming back and feeding it more targeting data. The next part of creating Google was a little easier because if they screwed it up the first time they get to try and try again until they succeed in building a money printing machine on the back of this hot-property-with-targeting-data that really does print money.

Facebook have the hot property that keeps users coming back and feeding it targeting data. They really screwed up the Ad network the first time they had a crack at it with Beacon. But, predictably, their users forgave them and they’ll keep having another crack at it until their money printing machine is running at optimum efficiency.

There are a few reasons I believe Facebook may be a bigger success than Google long term:

1. They have better data in the form of individual demographics, interests and data inferred from the social graph.
2. They already have a distributed network of sites in the form of Facebook Connect which has deeper integration than AdSense. That means Facebook gets more data about visitors to those sites than Google AdSense.

Possible risks:

1. Their management team doesn’t have Eric Schmidt. Eric spent years getting schooled by Microsoft when he ran Novell. So he has the hunger, the scar-tissue and battlefield awareness that you need to compete with juggernauts.
2. The hasbeen factor. Facebook has had a surprisingly good run and has proven to me it has legs because I’m still going back after a few years. But lets see if they can maintain that over the next decade.