I've been trying to send some hReview microformat data to all the different WP variants (hosted, wordpress.com and WPMU) via XMLRPC and your sanitizing code is breaking it in two different ways.
First is the ""WordPress should correct invalidly nested XHTML automatically" option which is actually re-writing valid safe XHTML. Obviously, turning this off should fix that but it means there are some bugs/undesirable behaviours in there.
It is taking:
<span class="reviewer vcard"><span class="fn">Conor</span></span>
and changing it to:
<span class="reviewer vcard"></span><span class="fn">Conor</span>
The second one is more important and it is that kses.php is stripping harmless class attributes and breaking the microformat markup. To allow hReviews to be posted, the following trivial change is required in kses.php.
In allowedposttags, abbr is currently listed as follows:
'abbr' => array ('title' => array ())
this just needs to change to:
'abbr' => array ('title' => array (), 'class' => array ())
Would you consider making this change to provide further support for microformats as you already do for XFN?
I'll continue to test the other microformats like hCard etc to see if they run into any problems.