From John Naughton‘s column in today’s Observer
By reading this, you agree to stop adding useless disclaimers
… consider the curious legalese that is increasingly appended at the foot of emails dispatched from corporate email servers. … A friend sends you an email saying “How about lunch?” and it comes with this implicit threat that if you so much as breathe a word of it to any living being the massed litigators of Messrs Sue, Grabbit and Runne will descend upon you. The practice is now so widespread that most of us have become inured to it. …
The funny thing is that the practice is, at best, legally dubious. “The value of disclaimers is limited,” writes Simon Halberstam (of Sprecher Grier Halberstam) in an article on weblaw.co.uk, “since the courts normally attach more weight to the substantive content of the communication and the circumstances in which it is made than to any disclaimer. Having said that, disclaimers may possibly be helpful if an issue ends up in court in various respects … and, since disclaimers cost (almost) nothing, it is worthwhile to use them.”
But don’t forget that, in Hedley Byrne & Co Ltd v Heller & Partners Ltd  AC 465,  UKHL 4 (28 May 1963), the case that established liability in principle for negligent misrepresentation, a disclaimer was effective!