Just installed WP 2.0.2, been using WP 1.5 for a while, anyways, I found the the new rich text editor in WP 2.0.2 generates some invalid Strict XHTML:
The rich text editor uses the <strike> tag for strikethrough. in XHTML Strict, the <strike> tag has been dropped. The rich text editor should be fixed to use the <del> tag instead, so it will validate Strict.
Also, I notice there is no underline button in the rich text editor and I believe there should be one, because it's there in the standard HTML editor. If an underline button is added, it should offcourse use the <ins> tag, not the deprecated <u> tag.
I went straight back to the standard HTML editor, but it would be nice to see it generate better XHTML for those wysywig people out there.