After some html tweaking, this blog is now almost valid xhtml. HTML validator shows 2nd page have only 1 warning. It had more than 100 warnings before my tweaking.
Homepage have 4 warnings, 2 of them are from video 'embed'. The others are from iframe and pagination. Iframe 'navbar' itself have 4 warning. These are google's faults which I can do nothing about. So I give up. Not that I think it's important, but it'd be nice if google generates valid xhtml code.