How do I use PHP to get the current year?

You can use either date or strftime. In this case I'd say it doesn't matter as a year is a year, no matter what (unless there's a locale that formats the year differently?)

For example:

<?php echo date("Y"); ?>

On a side note, when formatting dates in PHP it matters when you want to format your date in a different locale than your default. If so, you have to use setlocale and strftime. According to the php manual on date:

To format dates in other languages, you should use the setlocale() and strftime() functions instead of date().

From this point of view, I think it would be best to use strftime as much as possible, if you even have a remote possibility of having to localize your application. If that's not an issue, pick the one you like best.

<?php echo date("Y"); ?>

My super lazy version of showing a copyright line, that automatically stays updated:

&copy; <?php 
$copyYear = 2008; 
$curYear = date('Y'); 
echo $copyYear . (($copyYear != $curYear) ? '-' . $curYear : '');
?> Me, Inc.

This year (2008), it will say:

© 2008 Me, Inc.

Next year, it will say:

© 2008-2009 Me, Inc.

and forever stay updated with the current year.

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Or (PHP 5.3.0+) a compact way to do it using an anonymous function so you don't have variables leaking out and don't repeat code/constants:

© 
<?php call_user_func(function($y){$c=date('Y');echo $y.(($y!=$c)?'-'.$c:'');}, 2008); ?> 
Me, Inc.