Census forms began going out in the mail on March 17, 2010 and folks should be getting the shortly (if you haven't already). If you don't fill it out and mail it back, you will get a visit from government census takers sometime between April and August.
If you do get a visit from people claiming to be government census workers, be very cautious and don't assume they're who they say they are. If you have the means to verify their identity, do so (by calling your local census office).
DO NOT fill in any forms (or give out) that ask you for your social security number or bank account info. These are definitely fraudulent.
Census workers will NOT contact you via email either. So ignore any emails you get claiming to be from the Census Beareau.
I'd also recommend NOT inviting any strangers (including those claiming to be "government workers) into your home. If you do get a legitimate visit from Census workers, step out side and close the door to answer their questions. They don't need to be in your home and this just offers a bit of extra security in the event they're not who they say they are.
As always, just be aware and cautious when giving out personal information. Don't be a victim of a census scams!