CSS Class Based on Date
I recently saw a tutorial on SimplePie’s site about using relative dates and I modified the function to output a CSS class rather than text. That way you can make newer stories bold, brighter, or bigger and older stories dimmed out or smaller. Use your imagination with CSS. 
Here is the function
//CREATE CSS BASED ON DATE
function create_age_css_class($date_sent)
{
/**
$date_sent should be in the following format: YYYYMMDDHHMMSS
Based on doRelativeDate() By Garrett Murray, http://graveyard.maniacalrage.net/etc/relative/
**/
$in_seconds = strtotime(substr($date_sent,0,8).' '.
substr($date_sent,8,2).':'.
substr($date_sent,10,2).':'.
substr($date_sent,12,2));
$diff = time()-$in_seconds;
if ($diff < 86400)
$css_class = 'age_today';
else if ($diff < 604800)
$css_class = 'age_days';
else if ($diff < 1209600)
$css_class = 'age_week';
else if ($diff < 2630880)
$css_class = 'age_weeks';
else
$css_class = 'age_month';
return $css_class;
}
Here is how I call it
$data .= '<li><a href="'. $item->get_permalink();
//SET CLASS BASED ON DATE/AGE
$data .= ' class="' . create_age_css_class($item->get_date('YmdHis')) . '"';
$data .= '>';
You don’t have to use SimplePie for this function, but its what inspired me to modify it.