Sometimes, jumping from one branch of the family tree to another, one can loose a track of relation or navigation direction. For example, if one goes to a list of tree members (on Family Tree page) and open member X's personal page, then go to "View in tree" link, he or she could end up on family tree view page with member X as starting person and no trace how that person is connected to the principal one. One can always start form the beginning view of the tree, but it is not the point.
I think, it would be a great feature for the online tree to list the person's relation status to the principal person of the three (i.e. from the point of view of the person reviewing the tree after logging in). That relation status could be shown in the area where all personal data of the selected person are listed, for example, next to the picture below the name and years of birth and death but above the list of all pictures and events.
It becomes very important in big trees, where one could go too far from its own position to determine the relation visually or jump on tree branches that are displayed in their own pages without showing the principal person of the tree.
Further, it might be useful to indicate blood relatives on the tree (again more important in big trees) to help determine in which direction one should go from the given position on the tree to get back to him- or herself.
In addition, on pages that do not display the principal person of the tree, tree branch links that could lead to the principal person of the tree, should be marked somehow to indicate that.