Census Day/Night (England and Wales) is Saturday, 27 March, 2011. Yes I know it's over a year away but I may forget to give you this link. It analyses the questions.
Just for starters: did you know the data is to be collected by US Defense Contractor Lockheed-Martin? Don't we have data processors in the UK these days?
Scotland's Census will take place on 27 March, 2011 too. Some questions differ from the England and Wales version. Details can be found here.
Once you've read the information, don't forget there is a fine of £1,000 for providing false information. Of course, none of us would ever consider giving inaccurate information, so the threat of a fine will not apply.