If you add that you can use CSS for the section element in IE 8, which you couldn´t before. You can also add a reference to Modernizr which makes it automatically (I use Modernizr on my own webpage to make it possible to view it in IE 8):
Actually HTML5 supports both HTML and XHTML syntax. There is one important change since XHTML 1.1 though.
When using XHTML 1.1 you should use application/xhtml+xml as MIME Type, but when using HTML5 with XHTML syntax you
must use application/xhtml+xml.
That is a problem since pre-IE9 don´t support application/xhtml+xml. If you try to open it in IE 8 the browser asks you to download the file instead of displaying it in the browser. Because of this I use the "wrong" mime type at the moment at my personal
For my personal site which I´m building at the moment, I use HTML5 with XHTML syntax (view the source to se what´s new):