I tried out Free Mind - it's a really nice solution for creating mind maps, but it's not really appropriate when you have blocks of text. Shame really, it'd have been a familiar way to organise. For now I'm going to just adapt a mini website I made for work this week, shouldn't take long - I'll post some screenshots when I'm done, happy to provide the code (though the requirements of understanding html and having a server somewhere might be a bit of a barrier!)
Watched the vid and read a bit of the site, and I feel a bit ambivalent about it. It looks like it's got great performance and really smooth zooming, and I get the distinct impression it's a very well made piece of software. However, to me it looks more suited to rping itself than worldbuilding (though that could very easily be a false impression); there are a few things that appear to be missing from a worldbuilding point of view.
For example:
• How does it work with distortion due to map projections, and can you project the map onto a 3D globe instead of a flat rectangle?
• Can you use it to measure distances and areas?
• What happens if you rename linked files outside the program?
• Can you link between different text files?
• What about categorisation for ease of editing?
Obviously different people build worlds in completely different ways, so that list of issues is probably irrelevant to most people. I definitely agree with you that it makes a lot of sense to use an interactive map as the central hub for worldbuilding, just wondered how feasible it is. Currently, I have Google Earth for the 3D globe providing distance/area measurements (and G.Projector for exporting projected maps), and a load of disorganised crap for the text information - which I plan to organise asap. It's not ideal that they're separated from each other, but since I can open Google Earth on one screen to fly around the world at speed, and open my textual info on the other screen, it's hard to see a big efficiency gain from switching to ViewingDale.