When a link is selected, the tools label still says Thought, it would be nice if it said Link instead.
Also, under some color themes, the link label doesn't show, it just appears as a square. For example, use the Dark Grey Theme and enter a link label. Perhaps using the thought text color for the link label text also would resolve it?
Finally, I really like the curved links, and the movement that appears in the links when thoughts are highlighted. It helps identify directionality easily, and makes it easier to pick out which link belongs to which thought.