I spent some time to modify the flex theme (not done though), made it validate in xhtml 1.1 and all that, but there are certain glitches I can't fix as easily. Take a look at
In FF 1.0.4, the comments (of the currently one and only post) won't be displayed properly, IE6 and Opera8 work perfectly. Also, in IE6 the header is b0rked and in comments, the footer has an additional white line at the end which shouldn't be there. I tried tweaking it here and there but was unsuccessful.