It seems to me that howling something is a type of up-vote (reddit, hn, digg) or bookmark (delicious, xmarks). This means you have an idea of what people have found interesting. So why don't you tell what people what others find interesting in addition to or instead of saying what has been posted recently? One reason I can see for using most recent as your exploration metric is that it would really correspond to popularity, the most popular link would be most recent most frequently (depending on implementation). I don't think this is a good enough reason though, one person has the ability to use bursts of spam to remove things they don't want to be seen on the explore page (its harder to stay popular if nobody can see you so this means spamming is an effective way to give a down-vote).