こんなのとか

<?php
function pr($var) {
echo '<pre>'; print_r($var); echo '</pre>';
}
date_default_timezone_set('Asia/Tokyo');
header('Content-Type:text/html; charset=UTF-8');

$rss = simplexml_load_file("http://b.hatena.ne.jp/hotentry?mode=rss");
$localDateGroup = array();
foreach ($rss->item as $item) {
$dc = $item->children('http://purl.org/dc/elements/1.1/');
$link = $item->link;
$title = $item->title;
$date = (string)$dc->date;
$desc = $item->description;
$localDate = date('n月d日', strtotime($date));
$entryData = array($date => "<li><a href=\"$link\" title=\"$title\">$title</a>$date<p>$desc</p></li>\n");
if (!array_key_exists($localDate, $localDateGroup)) {
$localDateGroup[$localDate] = $entryData;
} else {
$localDateGroup[$localDate] += $entryData;
}
}
foreach ($localDateGroup as $localDate => $entries) {
krsort($entries);
echo $localDate;
echo '<ul>';
foreach ($entries as $date => $entry) {
echo $entry;
}
echo '</ul>';
}