I was interested to read your comments about Tinderbox (TB). As a Windows user I cannot evaluate this app though I have been to the website and studied all the screencasts, so I understand their jargon better now.
A TB Note is a rectangular box on their Map view, so is equivalent to PB's Thought in Expanded View. Clicking TB's Note opens it for editing.
In many ways, TB's interface offers many more user-friendly features than PB does - multiline note names, resizable Notes (equivalent to resizable Thought boxes in the plex), varying fonts and colors, a long list of attributes (metadata) for each Note, sorting by last word (surname), and views, views, views. Yet despite all this largesse, I began to feel Tinderboxed in after a while. As SteveZ observed in his blog, "the Map View in Tinderbox restricts you to one level of detail at a time".
When reading comparisons between PB and TB, it's not always clear which PB view is being used in the comparison. You said:
This addresses a challenge I've had with using PB as a mindmanager: The graphical layout is constrained by how PB shows things on the screen. TB, on the other hand, lets you lay things out in "Map" view any way you want...
That might be true of Normal view, but certainly not of Expanded View, where with a bit of experimentation you can create just about any layout you need (see my examples here). Mind you, this can be hard work at times as there are no intelligent agents, containers, adornments, etc. to help you, but on the plus side they don't get in the way of your creativity either. As you see I make a lot more use of orphan thoughts in these examples than I ever imagined I would, and simply grouping them without any attempt at linking them turned out to be extremely good for storyboarding my ideas.
My worry is that if I turned to Tinderbox now I might have to think the Tinderbox way in order to record my ideas, and right now this seems more constraining than using PB.
It would not take much for Harlan to make Expanded View the really user-friendly environment that it needs to be to compete with TB at its own game. My impression is that TB began largely as a map view and extended from there, whereas PB began as a database which excels at retrieving associations, hence Normal View. A map view looks very pretty but can become difficult to manage (scalability problems) as it grows huge, whereas users of PB can always fall back on Normal View to manage large databases and reserve Expanded View for those areas where intricate relationships become really important.