Web-site usability guru Jakob Nielsen has warned that many web sites are still full of errors, are unnecessarily complicated and include too much jargon. As a result, companies risk losing business and damaging their reputations. Nielsen's list of the top 10 common mistakes is available from the first URL below.

Nielsen advised companies to act quickly to improve service for users.

Referring to his own guide on homepage design and usability, Nielsen said that two-thirds of corporate web sites contained common mistakes. For example, many include too much marketing jargon and their navigational capabilities are often poor.

Many firms do appear to be making an effort to make their sites more user-friendly. Financial group Nationwide has redesigned its site to be more accessible to blind and partially-sighted users. However, other usability experts said that many recently revamped sites - including that of chip giant Intel, which has been redesigned to rely more heavily on text - do not follow good design principles.

Although the Intel site now relies less heavily on graphics and has become faster, experts argued there is room for further improvement. "It hasn't gone as far as it could," said Ian Lloyd, a web site designer and accessibility expert, citing poor support for partially-sighted readers.

Barney Barnes, managing director at web design firm Catalyst, said that when it comes to designing accessible sites the UK is moving slowly. "I am surprised that despite a legal obligation [for accessible sites] nothing has changed," he said.