Persue it. Upper case tags is an HTML standard not xhtml. Sounds to me like the site is written in HTML 4 transistional. In xhtml all tags need closing - even <br> should be closed in xhtml. Having said that there are a huge amount of sites on the web that aren't compliant. It will affect your rankings in Google. In the webmaster guidelines one of the first things that is mentioned is markup technical quality. They can only be referring to W3C standards. It may result in issues with some browsers. But then again some browsers don't comply with xhtml 1.0. The only way to be sure is testing. If you would like me to correct all the errors I can do so. Only a day or two work depending on the number of site pages and whether the html is generated using server side scripting. PM me if you need my help - rates are extremely competitive. Feel free to run my site through W3C compliance checking if you want proof I do what I say. Good luck.