I would find it useful if connected notes were highlighted when you have your mouse over a note. My boards quickly turn into spider webs and it would be useful to see where in the web the connections between notes go to.
In the example below, the user would have clicked on note 2, and then the connected notes are highlighted in blue along with the connection lines. This could be a toggled on or off. The second degree of separation connections could be shown in a different color tow so note 5 and note 4 could be highlighted in green.
I hope others would find this feature useful too.