curiousAnywho, while reading the page on Embedding LJ with PHP, something cought my eye. The last usage says you can use PHP includes, which can potentially be very harmful.
<?php
include "http://www.livejournal.com/customview.cgi".
"?username=darkain&styleid=101";
?>Because PHP will actually process the contents of the document, PHP can be inserted into the LJ and PHP will see it as code. This can be tested with making a post with either of the following methods:
<? echo 'test'; ?> or <?php echo 'test'; ?>
While this byself may not be harmless, as in theory only the person in control of the web site is in control of the journal as well, but if their LJ is ever comprimised, then it would easily be possible to take over their personal site as well.
My recomendations would be to completely remove the the suggestion of "include" from the page mentioned above, as well as to possibly disallow any tags that start with "<?" at all, as I know its also caused some issues in the past with some browsers falsly allowing JavaScript execution as well.