I like absolute links, especially in navigation. The reason is, I can use an include file and include the navigation in different folders on the web site, and the links will still work properly
It depnds. As jgjg said, on my top_content.php and bottom_content.php files, I use absolute links, but on the content pages I use relative links sometimes. I just got used to using absolute links.
Simple rule: use relative uri's wherever you can. There are few reasons why it is so but i'm lazy to explain.