If you type the site URI (ie http://www.davidarussell.co.uk/) into the W3C validator you’ll notice it goes a bit schizo at the CSS. Not to worry, the content style sheet is still entirely valid (as you’ll see by clicking on the sidebar link), the displeasure is caused by the fancy link titles I now have installed. To create the effect, they must use slightly different CSS for each browser (which of course is not part of the CSS standard). That way, all browsers get the same effect but the CSS does not validate. I think I can live with that.
EDIT: I’ve decided to pull the Nice Title stuff altogether. Invalid code is invalid.