To the people who say 'I have nothing to hide' I always respond with an example I saw reported on a few years ago. The ISPs in the UK were gathering data on users and giving it to police, they were searching for child porn users and terrorists.
Most people might find that acceptable, but what happened next was shocking; mistakes were made and the wrong people were implicated, this is as simple as [email protected] being mistakenly identified as [email protected]. People were having their front doors smashed in in 5AM raids, lead off in handcuffs etc. because of clerical errors. The problem is, these kinds of allegations dont simply go away, people become tarnished 'there is no smoke without fire', after all. People lost their families, jobs, homes and were ostracised by their communities, their lives were ruined.
The report was made by the UK Information Commissioner, and was only concerned with people whos lives had been severely effected.

So we do need a right to privacy, we dont want to be caught in a data dragnets by such unreliable sources as ISPs; their job is to provide your broadband, not to decide if you go to jail.