Spikes in demand for iOS downloads also puts stress on networks.
Apple users have reported difficulties accessing the company's new iCloud online service, which went online yesterday.
Some holders of Mobile Me accounts – Apple's existing online service – said they were unable to migrate to the new platform. Instead of accessing the new iCloud features, they were presented with a grey screen and the words "Please try again later". Apple has now created a status page where users can check for service availability.
The problem comes in the wake of Research in Motion's issues with its email service earlier this week. However, rather than a technical failure, Apple appears to be a victim of its own success, with too many Mobile Me users trying to migrate.
At the same time, network managers were reporting difficulties caused by internet traffic spikes, as Apple device users rushed to download iOS 5 for iPads and the iPhone. According to a report on the internet problems by The Guardian, service providers and internet hubs across Europe saw exceptionally large increases in download volumes. The iOS update weighs in at about 770MB.
But, although users appear to be frustrated at delays in downloading the new version of iOS and in moving to iCloud, predicting peak levels of demand for new services is an inexact science, said Bob Dowson, operations director at Site Confidence, the web performance testing division of NCC.
"If Apple can't anticipate the level of demand, then no-one can," he said. "You have to test, in advance, from an external user point of view to make sure your servers can cope with the spikes, but a higher level of testing will cost more money. And it is really easy to providers: if Apple gets it wrong, then anyone can." He added that higher than anticipated levels of demand for iOS have not, though, affected traffic on the wider internet to any noticeable degree.