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

• Simple Theme might have no friends defined. If you are Simple Theme, you can edit your LiveJournal friends so they show up here.
• Simple Theme 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.
• Simple Theme 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.