Tiggerito - 4:38 am on Jul 19, 2010 (gmt 0)
I personally go for relative, to keep the size down.
With CainIV's interesting experiment, and Angonasec comment on keywords I will keep my mind open.
An idea for keyword stuffing (don't try this at home)
I would hope search engines process the final path when gathering keywords so this is not possible.
Another possible negative for relative is that spiders can also get it wrong. Recently a spider (LexxeBot) has been trying to index pages that it has obviously miss calculated the absolute path to.