If you're located in the upper Midwest it's possible you're being affected by a major Internet outage caused by a fiber optic cable cut by construction equipment Wednesday in Illinois. This has caused a ripple effect as they've attempted to re-route traffic around the cut, so it's even affecting customers of other ISPs that didn't completely loose service.
Even if this isn't your specific issue, this kind of dropout can occur between you and another segment of the Internet at any time, so often it's not the server that's down, but rather something between you and the server.
The Internet as a whole is fairly resilient, but not nearly as infallible as you might have been led to believe.
Bitman