Facebook users in Europe were unable to access the site this morning. While the problem, which Facebook called "technical difficulties," was resolved quickly, it did lead to questions about what companies who rely on Facebook for user login to their own sites would do if there was a prolonged outage.

"The risks are apparent," said Jean-Paul Rehr, a co-founder of Waygoz.com, a game swapping site which has been using Facebook connect since launching its beta last fall. But Waygoz has no plans to drop the Facebook login and, when it launches in the U.S. in four weeks, users will only be able to log into the site using their Facebook credentials.

"When we introduced Facebook login about a month [after our launch], our conversions multiplied by a factor of four," Rehr said. "New user 'registration fatigue' is eliminated with single sign on (and)...there is 'instant credibility' for users when they see the Facebook button."

Today's outage lasted about two hours and affected Web site, smartphone and mobile users throughout Europe, including users in the U.K. But companies are seemingly willing to risk those outages and their possible impact on access to their own sites because of the ease of logging in and not having to remember passwords if they log in using Facebook or another social network, like Twitter.

Known as Facebook Connect, the login feature is increasingly becoming a standard option for many Web sites. Facebook hasn't tried to monetize the feature yet, and even if it continues to offer it without cost, it still helps keep users logged into the site. That, in turn, ncreases Facebook's reach and influence over the entire Internet.

Beyond the conversion rate, a Facebook log-in gives site users more user data and makes it easier for sites to tailor content to individuals.

"Strategically thinking, website owners shouldn't consider FB Connect as a security gate, but more like a huge database that holds personal information and interests of the site visitors," said Sultan Alsharif of iPad game maker Local Aliens LLC. "Using this information to deliver tailored content and services could impact how the Web delivers information and engage the visitor."

But in a Twitter post, angel investor Tariq Krim said companies should rethink the one login strategy that Facebook requires.

"Facebook two hours down time this morning may make us rethink our login strategy#facebookconnect, " he tweeted.