Should I update the copyright notice every January? as in
© ACME Corp 2011
I'm not asking about how or whether to claim copyright at all (that is dealt with here), but whether the year has any importance.
The date is supposed to be when it was published. So if content is ongoing then it could be a range or it could be the date of the most recent revision. If the site has had no changes then it should be the earliest date.
Some people prefer it to be recent to look fresh, others prefer to make it as long ago as possible to show they got there first. Basically there is no convention and as you mentioned in your question it means absolutely nothing legally so you can put whatever you like.
To my knowledge, JamesRyan is right in that it means nothing as legality goes. Having said that, I've found that it does tend to have an effect on users.
Back in the day, it was commonplace to indicate content freshness via the "Website Last Updated" blurb. Since that's no longer the rage, I've had many a user refer to using the copyright date as a rudimentary freshness check.
Bearing that in mind, I think it's prudent to keep it updated but there's no need to update it manually. It's pretty easy to handle with a bit of server code:
© 2009 – <?php echo date('Y'); ?> YourSite.com
The inclusion of the date is not mandatory in all countries, but the date, and the name, along with the symbol (legal device) form part of the formal assertion of rights. See: http://en.wikipedia.org/wiki/Copyright_notice