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

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