Frazzled users began posting urgent help messages on Christmas Day and Boxing Day on Apple's technical forum for iTunes. They complained they were not allowed into the "store" or were being told the system could not download songs and videos.

It was not immediately clear how many people were affected and Apple Computer would not comment on what caused the slowdown and whether it had been fixed. Analysts said the problems were probably caused by too many people trying to use the site at once - at some points over Christmas, four times as many as usual.

Some financial analysts said the delays could be a sign that sales of iPods and the like had dramatically exceeded Apple's own forecasts.

Apple commands about 75 per cent of the market for downloaded music, but could lose as much as five per cent of that market share in 2007 because of increased competition from rivals.

Error messages

Dan Frakes, a senior editor at Macworld magazine and www.playlistmag.com, a website focused on digital music, said he and some colleagues were unable to access the iTunes store or received error messages when they tried to download songs early this week.

However, others breezed through the process hassle-free and Frakes successfully downloaded songs later.

He said the problem was probably not as widespread as the grumbles of some frustrated new customers suggested.

"The store itself was working, there was just too much traffic," he said. "It's a good bet that most people were able to get through."

Analysts said they did not anticipate a rash of iPod returns because of the delays.

"What you're seeing is the tremendous success of the iPod," said Michael Gartenberg, vice-president and research director with JupiterResearch.

"No doubt it was a very, very popular gift.

"No matter how well you plan on the server side of the equation, there are always times when you get caught short."