To me, its inefficient to load the product in its whole when u can get a smaller option.
$this->helper('catalog/output')->productAttribute($_item, nl2br($_item->getDescription()), 'description');
The above would also do the trick and doesn't require loading the whole product object. The processing would be the same as short_description.
Yes, this isn't loaded by default but you can just use the attribute by enabling product listing on the attribute you need.
For the record, if you are planning on using larger descriptions you might want to cut them off. I usually do something like this:
<?php echo Mage::helper('core/string')->truncate($this->helper('catalog/output')->productAttribute($_item, nl2br($_item->getDescription()), 'description'),240) ?>
$_item->getDescription()
give you? – Mufaddal May 20 at 11:00