With over 350 million users registered, Facebook has some of its competitors in the digital identity space legitimately concerned that Facebook Connect could quickly and easily rule supreme as the ultimate agent for universal login access and sharing across networks.

This ominous and very real possibility necessarily provided the backdrop for Google's announcement Wednesday that it would be marrying its own Friend Connect service with Twitter account logins. Starting yesterday, users can now log in to any of the nine million Google Friend Connect-enabled sites with a Twitter user name and password.

Much in the same way that Facebook Connect sites allow for seamless transfer of updates and information exchange to Facebook from external sites, Google says that logging in to a Friend Connect site with a Twitter user name will automatically link the associated Twitter profile. As a result, tweeting to your followers about the third-party site should take nothing more than a click.

Though this may help Google flesh out its digital identity service a bit more, getting Twitter on board is small-time stuff compared to, say, partnering up with Facebook. And that's exactly what Yahoo did, as it announced on Wednesday that it will be integrating Facebook Connect into a plethora of Yahoo Web properties, like its Mail, News, Sports, and Finance sites. Because some of these properties boast memberships in the tens of millions, this is no small win for Facebook as well.

Check out this video of Google Friend Connect + Twitter in action.