Akismet plugin has a XHTML bug - does not validate (all realeases, long time ago).
Line 780 in version 2.5.1 should be:
<div id="akismetwrap"><div id="akismetstats"><a id="aka" href="http://akismet.com" title=""><?php printf( __( '%1$s %2$sspam comments%3$s %4$sblocked by%5$s<br />%6$sAkismet%7$s' ), '<span id="akismet1"><span id="akismetcount">' . $count . '</span>', '<span id="akismetsc">', '</span></span>', '<span id="akismet2"><span id="akismetbb">', '</span>', '<span id="akismeta">', '</span></span>' ); ?></a></div></div>
Bug: I the original plugin there is a <div> after an opened <a> - this is not valid.
Martin