There are a few reasons why you might not see posts on this friends page:

• Clark Kent might have no friends defined. If you are Clark Kent, you can edit your InsaneJournal friends so they show up here.
• Clark Kent might have friends defined, but all of their friend's posts might be over two weeks old (according to the times on our servers), and thus wouldn't be displayed here.
• Clark Kent might have friends defined that post only protected entries that you can't view, because they haven't defined you as a friend in return.