There are 14 themes in Moodle 1.6 beta. A quick search reveals that of these, only 3 use H1 to markup headermain: Chameleon, Oceanblue and Standard.

8 still use a 1-cell <table> to layout the navbar/breadcrumb trail, in header.html.

Also, 2 use a <table> for the navbar/breadcrumb trail, in footer.html: Oceanblue and Standard (not sure if these are ever displayed, but better fix them).

To the theme maintainers who have implemented accessibility Markup changes, well done. It would be great if the rest could follow suit, thanks.