Well that kind of said it all, really.
I decided to make the move over to strict xhtml, from transitional. In the process I removed the del.icio.us bookmark link that I’d added a while back and was causing the page to fail the validation. I probably could have fixed it, but I wasn’t in the mood, and it was pretty useless for my site anyway. If you used del.icio.us you’d more than likely have the bookmark to hand anyway.