With intense and widespread interest in the ceremonies and festivities, especially President Obama's oath of office and inaugural address, millions of people had been expected to tune in online, especially those without TV access while at work.

Big media, news and U.S. government sites streamed events live and prepared special sections for the inauguration, yet some were still caught off-guard and experienced performance problems, mostly between midmorning and 12:30 p.m. U.S. Eastern Time.

Among those experiencing significant slowdowns were the sites of ABC, CBS, Fox Business, the L.A. Times, NBC, National Public Radio, USA Today and The Wall Street Journal, according to Keynote Systems, an Internet measurement and testing company. Government sites that buckled under the traffic included those of the White House, the U.S. Senate and the National Park Service, according to Keynote. Gomez, another Web performance-tracking company, also noticed a performance problem at the National Public Radio Web site.

"We predicted today would be one of the most, if not the most, significant online streaming event[s]," said Shawn White, Keynote's director of external operations.

"This was an unprecedented online event. I don't think we've ever seen as many viewers go online to watch an event," he added. "It's difficult to prepare for something that's unprecedented."