The real problem isn't now, it's what may happen with this law in the future.
Sure, most people have 'nothing to hide' (usually wrong, most people only follow the laws that it suits them to obey), but what happens if the government changes, as it is wont to do, to a far more sinister one?
The BNP have been gaining momentum, and while it may ultimately lead nowhere, you must remember that Labour got into power without a majority of the votes last time around. A government may decide that what is now merely innocuous banter about how silly they're being is actually dissent, and there are many places today where political dissent carries a far higher penalty than it does in Britain.
Same problem with I.D. cards. Far as I remember, in the Identity Cards Act 2006 specifies a whole range of information that can be stored in the database, and it doesn't take much for someone to change it so it says, for instance, your sexuality. If we find ourselves in the clutches of a considerably more fascist regime than we are now, one can imagine the uses to which they would put them.
But hey, as long as we're stopping those bloody terrorists, right?