Export your Personal Brain (with link types) to a PersonalBrain XML file and use the Excel XML import function and import the PB xml in the Excel-2007 sheet (see ZIP file below).

Analyze your PB link relationships with this excel import sheet

As you will notice, there is a need for links with a direction reading from left to right.

See also, Typed links have a direction
http://thebrain.uservoice.com/pages/general/suggestions/83489
advance Link types
http://forums.thebrain.com/tool/post/thebrain/vpost?id=2418770
more advance Link types
http://thebrain.uservoice.com/pages/general/suggestions/74550

Suggestion for Harlan and the PB team, if you don't want arrowheads in the plex you can put the name of the left-thought, the link-type and the right-thought together in one link label, see picture below !!

When you can see the direction of the link in PB there is another need, a simple way for changing the direction of the link.