Is there a way to tell IE8 to trust all sites by default ? I know that could be a security issue but browsing is controlled by the (transparent) proxy anyway.
So users cannot use a site or part of it until they put the site in the trusted list and for not so experienced users that is an issue.
Normal public web sites are not the problem. The problems begin on web "applications": bank, webmail, tax authority. Not all, but some and after putting them into trusted sites it is working.