According to AlertSite, a Web performance management company, between 6 a.m. and 1 p.m. ET Thursday, one portion of the Reddit site took more than 60 seconds to load, only to return an error message. Foursquare’s homepage had 84.44% availability between 8:15 a.m. and noon, also returning error messages explaining the downtime and slowness.

At 5:16 a.m. ET Thursday, site administrators reported that they were dealing with connectivity issues impacting Amazon’s Relational Database Service, which is used to manage a cloud database, across multiple zones in the Eastern United States.

That means some Web sites were down or partially disabled for at least 11 hours.

While that’s a problem for the downed sites, it’s probably going to be tougher on Amazon itself, according to Robert Mahowald, an analyst with IDC. “Amazon is held as a paradigm of operational uptime,” he said. “When this kind of thing happens, it definitely sends a chill through the whole cloud and hosted services industry…. It’s absolutely a black eye. There’s no doubt about it.”