Michael Heilemann said it succinctly two years ago when he explained that pagination navigation should have newer stuff on the right, and older stuff on the left.
Consider a blog like a diary. You start writing on the first page and then go towards the right. And since the first page of a blog is the latest entry, to go to the older entries, you have to press the arrow that points to the left.
Left = Old.
He's got it right, and Wordpress (among others) has it wrong. I love Wordpress, and in order to help Wordpress users fix the code in their themes, here's some sample code that corrects Wordpress's default pagination navigation:
For pages with single entries:
<div class="left"><?php previous_post('« %','','yes') ?></div>
<div class="right"><?php next_post(' % »','','yes') ?></div>
And somewhat confusingly, for pages with multiple entries you should have the following:
<div class="left"><?php next_posts_link('previous', 0) ?></div>
<div class="right"><?php previous_posts_link(' newer', 0) ?></div>
This intuitive idiom is important enough to get right, despite the fact that Wordpress's backwards implementation has gained some traction.