I have often wondered just how much real difference XHTML standard adherance makes
On a fast desktop computer, probably not that much. On a slower machine a standards-compliant browser like Firefox ought to render pages more quickly, as there won't be any processing required to fallback onto quirks mode: on my EeePC 701 the site certainly
feels quicker.
On mobile devices I suspect it
does make a difference - the site now loads on my iPAQ, which it wouldn't before.
If nothing else, you should now have that nice warm glow of a job well done
Now all you have to do is get rid of the 26 or so problems that stop it validating as XHTML 1.0 Strict