Evan Schuman's StorefrontBacktalk

With its sites being unavailable for barely one hour over four months, MySpace has the best uptime of any major social networking site and Twitter (more than 37 hours of downtime during the same period) has the worst.

Those stats come courtesy of Pingdom’s periodic uptime surveys, which tracked some 16 social networking sites from January 1 through April 30 of this year.

Leading site MySpace had the least downtime, achieving an uptime percent of 99.96 with its one hour and five minutes of downtime. Facebook was several notches below MySpace, with 2 hours and 29 minutes of downtime and a 99.91 percent uptime rating.

Not only was Twitter’s 37 hours and 16 minutes of downtime the worst in the group, it was almost double the amount of downtime from the second worst-performing site (Reunion.com, with 18 hours and 55 minutes of downtime). But even Twitter’s numbers amounted to an uptime that sounded good: 98.72 percent. Pingdom’s Peter Alguacil said those percentages can be misleading.

"A 99 percent uptime may sound like much, and this is a rather common misconception. But if you do the math, it means that your site will be unavailable for more than 7 hours in a 30-day month," Alguacil said. "For an e-tailer, losing 7 hours of sales in a month isn’t a very good thing, not to mention what happens to customer trust when they visit your site and find it unavailable. The 98.72 percent average uptime that Twitter had in January through April is the equivalent of more than 9 hours of downtime. That’s roughly an entire workday."

Asked what he would consider an acceptable—as opposed to a good—figure, Alguacil said about 99.5 percent uptime, which is about 3 hours and 36 minutes of being down. "I think that could be considered a kind of ‘lower acceptable boundary.’ If you find your uptime consistently slipping under this, you have a problem," he said.

Other sites tracked were Reunion, Pownce, Bebo, Hi5, Windows Live Spaces, LinkedIn, Friendster, Last.fm, Orkut, Facebook, Classmates.com, Yahoo 360, LiveJournal and Xanga.