I like Treemaps a lot, though currently I’m having problems with them.
In general, I use them with quotations from sources (created in Sente and exported to DevonThink via the Finder, and thence to Tinderbox). I find they work really well when I have given the notes good titles rather than the default ones created by Sente from the first several words of the quotations, and if the text is quite small to enable display of longish titles. I’m able to look at the relevant part of the document and get a good grasp of the content of the source in quite a short space of time, while drilling down into details as necessary by selecting one of the notes.
Though I’m very happy with them (in principle) as they are now, I’m sure that understanding them better would enable me to make them even more useful to me.